Fundamental Theorem of Algebra for Quadratics

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Algebra 2 › Fundamental Theorem of Algebra for Quadratics

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1

A quadratic equation has the form $ax^2+bx+c=0$ with real coefficients. In $\mathbb{C}$, every quadratic has exactly 2 solutions counting multiplicity (two distinct real, one repeated real with multiplicity 2, or two complex conjugates). For $x^2+4x+4=0$, use the discriminant $b^2-4ac$ to predict the solution type and state the solutions counting multiplicity.

Which statement is correct?

There is exactly 1 solution in $\mathbb{C}$ because the quadratic is a perfect square

Discriminant $<0$, so there are two complex conjugate solutions: $x=-2\pm 2i$

Discriminant $=0$, so there is one repeated real solution: $x=-2$ with multiplicity 2 (total of 2 solutions counted with multiplicity)

Discriminant $>0$, so there are two distinct real solutions: $x=-2$ and $x=2$

Explanation

This question tests your understanding of the Fundamental Theorem of Algebra as applied to quadratics: every quadratic equation has exactly 2 solutions in the complex number system when counting multiplicity (repeated roots counted by how many times they appear). The Fundamental Theorem of Algebra states that every polynomial of degree n has exactly n complex zeros counting multiplicity. For quadratics (degree 2), this means exactly 2 solutions always—no exceptions! The type of solutions depends on the discriminant b² - 4ac: (1) if positive, two distinct real solutions, (2) if zero, one real solution with multiplicity 2 (like x = 3 counted twice from (x - 3)²), (3) if negative, two complex conjugate solutions. For x² + 4x + 4 = 0, let's verify exactly 2 complex solutions: (1) Calculate discriminant: b² - 4ac = 16 - 16 = 0 (zero). (2) This means 1 real solution with multiplicity 2. (3) Notice x² + 4x + 4 = (x + 2)² = 0, giving x = -2 with multiplicity 2. (4) Count: 2 solutions (one value appearing twice). Choice B correctly recognizes that a zero discriminant means one repeated real solution with multiplicity 2, giving the total count of 2 required by the Fundamental Theorem. Choice A incorrectly claims positive discriminant and two distinct solutions—but (x + 2)² = 0 clearly gives only x = -2 repeated! Choice C incorrectly claims negative discriminant and complex solutions when the perfect square factorization shows real solutions. Choice D makes the critical error of counting a repeated root as only 1 solution total, violating the Fundamental Theorem which requires counting multiplicity. Solution counting with multiplicity: (1) When discriminant = 0, the quadratic is a perfect square. (2) Factor as a(x - r)² = 0, giving solution r with multiplicity 2. (3) Count that value twice: one distinct value, but 2 total solutions. (4) This maintains the requirement of exactly 2 solutions for degree 2. Perfect square recognition: ax² + bx + c with discriminant 0 can be written as a(x - h)² where h = -b/(2a). The repeated root appears twice in the factorization, so we count it twice!

2

Factor the quadratic $x^2+25$ over the complex numbers. Recall: every quadratic $ax^2+bx+c=0$ has exactly 2 complex solutions counting multiplicity (either 2 real, 1 repeated real counted twice, or 2 complex conjugates).

Which option gives the correct factorization over $\mathbb{C}$ and the zeros?

$x^2+25=(x+5)(x-5)$; zeros: $5,-5$

$x^2+25=(x+25i)(x-25i)$; zeros: $25i,-25i$

It cannot be factored over $\mathbb{C}$ because it has no real roots

$x^2+25=(x+5i)(x-5i)$; zeros: $5i,-5i$

Explanation

This question tests your understanding of the Fundamental Theorem of Algebra as applied to quadratics: every quadratic equation has exactly 2 solutions in the complex number system when counting multiplicity (repeated roots counted by how many times they appear). The Fundamental Theorem of Algebra states that every polynomial of degree n has exactly n complex zeros counting multiplicity. For quadratics (degree 2), this means exactly 2 solutions always—even when there are no real solutions! To factor x² + 25, we need to find its zeros by solving x² + 25 = 0, which gives x² = -25. Taking square roots: x = ±√-25 = ±5i (since √-25 = √25 · √-1 = 5i). Therefore, x² + 25 = (x - 5i)(x - (-5i)) = (x - 5i)(x + 5i), with zeros at 5i and -5i. Choice B correctly identifies the factorization (x + 5i)(x - 5i) with zeros 5i and -5i—note that these are complex conjugates, as required for a real-coefficient quadratic. Choice A incorrectly factors as (x + 5)(x - 5) = x² - 25, not x² + 25—this is the difference of squares formula used backwards! Choice C has the wrong zeros (25i instead of 5i), arising from the error √25 = 25. Choice D incorrectly claims no factorization is possible over ℂ, but the Fundamental Theorem guarantees every polynomial factors completely over the complex numbers! Factoring with complex zeros: (1) Set the quadratic equal to zero and solve for x. (2) For x² + k² = 0, the zeros are ±ki (pure imaginary). (3) Write as product of linear factors: (x - zero₁)(x - zero₂). (4) Verify by expanding: (x - ki)(x + ki) = x² - (ki)² = x² - k²i² = x² + k². Sum and difference patterns: x² + k² = (x + ki)(x - ki) (sum of squares factors over ℂ), while x² - k² = (x + k)(x - k) (difference of squares factors over ℝ). The key difference is that sum of squares requires complex factors!

3

Which example correctly represents the case of a quadratic having exactly 2 solutions in the complex numbers but only 1 distinct solution value because it has multiplicity 2? (Recall: for $ax^2+bx+c=0$, the discriminant $b^2-4ac$ determines whether there are 2 distinct real solutions, 1 repeated real solution counted twice, or 2 complex conjugates.)

$x^2+4=0$ has solutions $2i$ and $-2i$

$(x-3)^2=0$ has solution $x=3$ with multiplicity 2

$x^2-5x+6=0$ has solutions $2$ and $3$

$x^2+1=0$ has one solution $i$ (multiplicity 1)

Explanation

This question tests your understanding of the Fundamental Theorem of Algebra as applied to quadratics: every quadratic equation has exactly 2 solutions in the complex number system when counting multiplicity (repeated roots counted by how many times they appear). The Fundamental Theorem of Algebra states that every polynomial of degree n has exactly n complex zeros counting multiplicity. For quadratics (degree 2), this means exactly 2 solutions always—no exceptions! The type of solutions depends on the discriminant b² - 4ac: (1) if positive, two distinct real solutions, (2) if zero, one real solution with multiplicity 2, (3) if negative, two complex conjugate solutions. But in all cases, counting multiplicity gives exactly 2 total! This highlights the repeated root case: one distinct value but counted twice. Choice C correctly shows (x-3)²=0 with x=3 multiplicity 2, giving 2 solutions but 1 distinct. Choice D miscounts x²+1=0 as one solution i (mult1), but it's two: i and -i, distinct. Strategy: identify zero discriminant for repeats, count multiplicity as exponent in factoring. Fantastic work—you're nailing multiplicity!

4

A quadratic with real coefficients has the form $ax^2+bx+c=0$ and always has exactly 2 complex solutions counting multiplicity (2 distinct real, 1 repeated real, or 2 complex conjugates). Suppose a real-coefficient quadratic has one solution $2+3i$. What must the other solution be, and why?

$2-3i$, because non-real solutions of real-coefficient quadratics occur in complex conjugate pairs.

There is no second solution, because a quadratic can have only one complex root.

$-2-3i$, because you negate both parts to get the other root.

$2+3i$ again, because complex roots cannot repeat.

Explanation

This question tests your understanding of the Fundamental Theorem of Algebra as applied to quadratics: every quadratic equation has exactly 2 solutions in the complex number system when counting multiplicity (repeated roots counted by how many times they appear). The Fundamental Theorem of Algebra states that every polynomial of degree n has exactly n complex zeros counting multiplicity. For quadratics (degree 2), this means exactly 2 solutions always—no exceptions! The type of solutions depends on the discriminant b squared - 4ac: (1) if positive, two distinct real solutions, (2) if zero, one real solution with multiplicity 2, (3) if negative, two complex conjugate solutions. But in ALL three cases, counting multiplicity gives exactly 2 total! This is why we can always factor quadratics as a(x - r1)(x - r2) even if r values are complex or repeated. For a real-coefficient quadratic with one solution 2 + 3i, the other must be 2 - 3i, as non-real roots come in conjugate pairs to ensure real coefficients. Choice A correctly recognizes that quadratics always have exactly 2 complex solutions when counting multiplicity and properly identifies the conjugate pair requirement for real coefficients. Choice D says no second solution because a quadratic can have only one complex root—this fails because the theorem guarantees exactly 2, and for real coefficients, complex roots pair up as conjugates; you can't have just one. To apply this transferable strategy: (1) If given one complex root for real-coefficient quadratic, the other is its conjugate (flip imaginary sign). (2) Verify by plugging in or using Vieta's formulas. For example, if root is 4 + i, other is 4 - i. You're building strong skills—keep going!

5

Use the discriminant to determine the solution type for $x^2-5x+6=0$. Remember: every quadratic $ax^2+bx+c=0$ has exactly 2 complex solutions counting multiplicity (2 distinct real, 1 repeated real, or 2 complex conjugates), and the discriminant $b^2-4ac$ determines which case. Which statement is correct?

Since it is a quadratic, it could have 0, 1, or 2 complex solutions depending on the discriminant.

The discriminant is positive, so there are two distinct real solutions (2 total solutions).

The discriminant is $0$, so there is one repeated real solution.

The discriminant is negative, so the solutions are a complex conjugate pair.

Explanation

This question tests your understanding of the Fundamental Theorem of Algebra as applied to quadratics: every quadratic equation has exactly 2 solutions in the complex number system when counting multiplicity (repeated roots counted by how many times they appear). The Fundamental Theorem of Algebra states that every polynomial of degree n has exactly n complex zeros counting multiplicity. For quadratics (degree 2), this means exactly 2 solutions always—no exceptions! The type of solutions depends on the discriminant b squared - 4ac: (1) if positive, two distinct real solutions, (2) if zero, one real solution with multiplicity 2, (3) if negative, two complex conjugate solutions. But in ALL three cases, counting multiplicity gives exactly 2 total! This is why we can always factor quadratics as a(x - r1)(x - r2) even if r values are complex or repeated. For x squared - 5x + 6 = 0, discriminant = 25 - 24 = 1 (positive), so two distinct real solutions (x=2, x=3), totaling 2. Choice C correctly recognizes that quadratics always have exactly 2 complex solutions when counting multiplicity and properly identifies the distinct real case from positive discriminant. Choice D says it could have 0, 1, or 2 complex solutions depending on discriminant—this is misleading; over complexes, always exactly 2 total (which may be real or complex). To apply this transferable strategy: (1) Compute discriminant. (2) Positive means two distinct real. (3) Solve via factoring or formula. For example, x squared - 3x + 2 = (x-1)(x-2). You're doing amazingly—practice more!

6

A quadratic with real coefficients (of the form $ax^2+bx+c=0$) always has exactly 2 complex solutions counting multiplicity. If its discriminant is negative, the solutions are non-real and come in complex conjugate pairs. If $2+3i$ is a solution of such a quadratic, what must the other solution be?

$-2-3i$

$-2+3i$

$2+3i$ (the same root again, not counted twice)

$2-3i$

Explanation

This question tests your understanding of the Fundamental Theorem of Algebra as applied to quadratics: every quadratic equation has exactly 2 solutions in the complex number system when counting multiplicity (repeated roots counted by how many times they appear). The Fundamental Theorem of Algebra states that every polynomial of degree n has exactly n complex zeros counting multiplicity. For quadratics (degree 2), this means exactly 2 solutions always—no exceptions! The type of solutions depends on the discriminant b² - 4ac: (1) if positive, two distinct real solutions, (2) if zero, one real solution with multiplicity 2, (3) if negative, two complex conjugate solutions. But in all cases, counting multiplicity gives exactly 2 total! For a real-coefficient quadratic with one complex root like 2 + 3i, the other must be its conjugate 2 - 3i to maintain real coefficients, ensuring exactly two solutions. Choice A correctly identifies 2 - 3i as the other solution, leveraging the conjugate pair property. Choice D tempts by suggesting the same root again, but that's incorrect—conjugates are distinct unless imaginary part is zero, and multiplicity would still require proper counting. To master this, remember: for real coefficients, non-real roots come in p + qi and p - qi pairs; if you know one, flip the sign of i-term for the other. Great job exploring this—you're unlocking the beauty of complex numbers!

7

Solve $x^2-8x+16=0$ in the complex numbers. Recall: every quadratic $ax^2+bx+c=0$ has exactly 2 complex solutions counting multiplicity. When $b^2-4ac=0$, there is one repeated real solution with multiplicity 2. Which answer correctly lists the solution(s) and multiplicity?

$x=4$ and $x=-4$ (two distinct real solutions)

$x=4$ with multiplicity 2 (so 2 solutions counting multiplicity)

$x=4$ (only one solution total)

$x=4\pm 4i$ (two complex solutions)

Explanation

This question tests your understanding of the Fundamental Theorem of Algebra for quadratics: every quadratic has exactly 2 complex solutions counting multiplicity, especially emphasizing repeated roots. The Fundamental Theorem of Algebra states that every polynomial of degree n has exactly n complex zeros counting multiplicity. For quadratics (degree 2), this means exactly 2 solutions always—no exceptions! The type of solutions depends on the discriminant b² - 4ac: (1) if positive, two distinct real solutions, (2) if zero, one real solution with multiplicity 2, (3) if negative, two complex conjugate solutions. But in ALL three cases, counting multiplicity gives exactly 2 total! For x² - 8x + 16 = 0, discriminant = 64 - 64 = 0, so x = 8/2 = 4 with multiplicity 2, or (x - 4)² = 0. Choice A correctly includes multiplicity for the count of 2. Choice B is a tempting distractor treating it as only one total, ignoring multiplicity— but FTA requires counting repeats! For zero discriminant, recognize the repeated root and count it twice. Factor to see the multiplicity directly. Super work—you're nailing multiplicity!

8

A quadratic with real coefficients has the form $ax^2+bx+c=0$. In the complex numbers, it always has exactly 2 solutions counting multiplicity, and if it has a nonreal complex solution then the solutions occur in conjugate pairs. If $2+3i$ is a solution of a quadratic with real coefficients, what must the other solution be (so that there are exactly 2 complex solutions counting multiplicity)?

$-2+3i$

$2-3i$

$2+3i$ (the same root must repeat)

$-2-3i$

Explanation

This question tests your understanding of the Fundamental Theorem of Algebra for quadratics: every quadratic has exactly 2 complex solutions counting multiplicity, and for real coefficients, nonreal solutions come in conjugate pairs. The Fundamental Theorem of Algebra states that every polynomial of degree n has exactly n complex zeros counting multiplicity. For quadratics (degree 2), this means exactly 2 solutions always—no exceptions! The type of solutions depends on the discriminant b² - 4ac: (1) if positive, two distinct real solutions, (2) if zero, one real solution with multiplicity 2, (3) if negative, two complex conjugate solutions. But in ALL three cases, counting multiplicity gives exactly 2 total! If 2 + 3i is a solution to a real-coefficient quadratic, the other must be its conjugate 2 - 3i to ensure real coefficients and exactly 2 solutions. Choice A correctly identifies this conjugate pair principle. Choice D is a tempting distractor because it suggests the same root repeats, but that's for multiplicity in real repeated roots, not for distinct complex ones; complexes must pair as conjugates. To find the other root, simply flip the sign of the imaginary part—it's that straightforward due to coefficient symmetry. Remember, this only applies to real coefficients; if coefficients were complex, pairs aren't guaranteed. You're making excellent progress—keep applying these rules!

9

Which statement best matches the “Fundamental Theorem for quadratics” idea: a degree-2 polynomial $ax^2+bx+c$ has exactly 2 complex zeros counting multiplicity, with the discriminant $b^2-4ac$ determining whether they are 2 distinct real, 1 repeated real, or 2 complex conjugates? (This also previews the Fundamental Theorem of Algebra: degree $n$ has $n$ complex zeros counting multiplicity.)

A quadratic always has exactly 2 real solutions, because complex numbers are not needed.

A quadratic has exactly 1 solution if it touches the $x$-axis and 2 solutions only if it crosses.

A quadratic can have 0, 1, 2, or 3 complex solutions depending on the discriminant.

A quadratic always has exactly 2 complex solutions counting multiplicity; the discriminant only changes the type (real distinct, repeated, or complex conjugates).

Explanation

This question tests your understanding of the Fundamental Theorem of Algebra as applied to quadratics: every quadratic equation has exactly 2 solutions in the complex number system when counting multiplicity (repeated roots counted by how many times they appear). The Fundamental Theorem of Algebra states that every polynomial of degree n has exactly n complex zeros counting multiplicity. For quadratics (degree 2), this means exactly 2 solutions always—no exceptions! The type of solutions depends on the discriminant b squared - 4ac: (1) if positive, two distinct real solutions, (2) if zero, one real solution with multiplicity 2, (3) if negative, two complex conjugate solutions. But in ALL three cases, counting multiplicity gives exactly 2 total! This is why we can always factor quadratics as a(x - r1)(x - r2) even if r values are complex or repeated. The core idea is that over complexes, every quadratic has precisely 2 zeros counting multiplicity, with discriminant just specifying the flavor. Choice B correctly recognizes that quadratics always have exactly 2 complex solutions when counting multiplicity and properly identifies how discriminant affects type, not count. Choice A says 0,1,2, or 3 complex solutions depending on discriminant—this overstates variability; always exactly 2 total (real count as complex with zero imaginary part). To apply this transferable strategy: (1) Remember the theorem guarantees n roots for degree n. (2) Use discriminant for type. (3) Count with multiplicity. For cubics, always 3, etc. You've got this—super progress!

10

Show that $x^2-4x+5=0$ has exactly 2 complex solutions counting multiplicity (as every quadratic $ax^2+bx+c=0$ does in $\mathbb{C}$). Use the discriminant $b^2-4ac$ to determine the type, then find the solutions.

Which option is correct?

Exactly one complex solution: $x=2+i$

Two distinct real solutions: $x=2\pm 1$

Two complex conjugate solutions: $x=2+i$ and $x=2-i$

One repeated real solution: $x=2$ with multiplicity 2

Explanation

This question tests your understanding of the Fundamental Theorem of Algebra as applied to quadratics: every quadratic equation has exactly 2 solutions in the complex number system when counting multiplicity (repeated roots counted by how many times they appear). The Fundamental Theorem of Algebra states that every polynomial of degree n has exactly n complex zeros counting multiplicity. For quadratics (degree 2), this means exactly 2 solutions always—no exceptions! The type of solutions depends on the discriminant b² - 4ac: (1) if positive, two distinct real solutions, (2) if zero, one real solution with multiplicity 2, (3) if negative, two complex conjugate solutions. For x² - 4x + 5 = 0, let's verify exactly 2 complex solutions: (1) Calculate discriminant: b² - 4ac = 16 - 20 = -4 (negative). (2) This means 2 complex conjugate solutions (not real). (3) Using quadratic formula: x = (4 ± √-4)/2 = (4 ± 2i)/2 = 2 ± i. (4) Solutions: 2 + i and 2 - i (two complex conjugates). Count: 2 solutions. Choice A correctly recognizes that the negative discriminant yields two complex conjugate solutions 2 + i and 2 - i. Choice B incorrectly claims positive discriminant and real solutions 2 ± 1 = 3 and 1, but we can verify these don't work: 3² - 4(3) + 5 = 9 - 12 + 5 = 2 ≠ 0. Choice C incorrectly claims zero discriminant and repeated real solution. Choice D violates the Fundamental Theorem by claiming only one complex solution—complex solutions of real-coefficient quadratics must come in conjugate pairs! Verification technique: (1) Always check your solutions by substitution. (2) For x = 2 + i: (2 + i)² - 4(2 + i) + 5 = 4 + 4i - 1 - 8 - 4i + 5 = 0 ✓. (3) Complex arithmetic: (a + bi)² = a² + 2abi + (bi)² = a² - b² + 2abi. (4) Both solutions must check out for the answer to be correct. Complex conjugate theorem: For polynomials with real coefficients, complex roots come in conjugate pairs. This maintains real coefficients when the polynomial is expanded from its factored form!

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