ACT Math : Squaring / Square Roots / Radicals

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1 : How To Find The Square Of Difference

\(\displaystyle \small (3a-2b)^{2}\) can be rewritten as:

Possible Answers:

\(\displaystyle \small 9a^{2}+12ab+4b^{2}\)

\(\displaystyle \small 9a^{2}-4b^{2}\)

\(\displaystyle \small 9a^{2}+4b^{2}\)

\(\displaystyle \small 9a^{2}-6ab+4b^{2}\)

\(\displaystyle \small 9a^{2}-12ab+4b^{2}\)

Correct answer:

\(\displaystyle \small 9a^{2}-12ab+4b^{2}\)

Explanation:

Use the formula for solving the square of a difference, \(\displaystyle \small (x-y)^{2}=x^{2}-2xy+y^{2}\) . In this case, \(\displaystyle \small \small \small (3a-2b)^{2}=9a^{2}-12ab+4b^{2}\)

Example Question #2 : Square Of Difference

Expand:

\(\displaystyle (2x-6)^2\)

Possible Answers:

\(\displaystyle 4x^2-12x+36\)

\(\displaystyle 4x^2-24x+36\)

\(\displaystyle 2x^2-12x+24\)

\(\displaystyle 4x-12\)

Correct answer:

\(\displaystyle 4x^2-24x+36\)

Explanation:

To multiply a difference squared, square the first term and add two times the multiplication of the two terms. Then add the second term squared.

\(\displaystyle (2x^)^2+2(2x)(-6)+(-6)^2=4x^2-24x+36\)

Example Question #1 : Squaring / Square Roots / Radicals

The expression  \(\displaystyle \frac{x^2-25}{x^2+11x+30}\) is equivalent to:

Possible Answers:

\(\displaystyle \frac{x-6}{x-5}\)

\(\displaystyle x+6\)

\(\displaystyle \frac{x-5}{x+6}\)

\(\displaystyle \frac{x+5}{x-6}\)

\(\displaystyle \frac{x+6}{x+5}\)

Correct answer:

\(\displaystyle \frac{x-5}{x+6}\)

Explanation:

First, we need to factor the numerator and denominator separately and cancel out similar terms. We will start with the numerator because it can be factored easily as the difference of two squares. 

\(\displaystyle x^2 - 25 = (x + 5)(x - 5)\)  

Now factor the quadratic in the denominator.

\(\displaystyle x^2 + 11x + 30 = (x + 5)(x + 6)\)

Substitute these factorizations back into the original expression.

\(\displaystyle \frac{(x+5)(x-5)}{(x+5)(x+6)}\)

The \(\displaystyle (x+5)\) terms cancel out, leaving us with the following answer:

\(\displaystyle \frac{x-5}{x+6}\)

Example Question #1 : Squaring / Square Roots / Radicals

Evaluate the following expression:

\(\displaystyle 2^{5}+(5*2)^{2}\)

Possible Answers:

\(\displaystyle 164\)

\(\displaystyle 61\)

\(\displaystyle 52\)

\(\displaystyle 110\)

\(\displaystyle 132\)

Correct answer:

\(\displaystyle 132\)

Explanation:

2 raised to the power of 5 is the same as multiplying 2 by itself 5 times so:

25 = 2x2x2x2x2 = 32

Then, 5x2 must first be multiplied before taking the exponent, yielding 102 = 100.

100 + 32 = 132

 

Example Question #1 : How To Find The Square Of A Sum

Expand:

\(\displaystyle (3x+5)^2\)

Possible Answers:

\(\displaystyle 9x^2+30x+25\)

\(\displaystyle 6x+10\)

\(\displaystyle 9x^2+25\)

\(\displaystyle 9x^2-30x+25\)

Correct answer:

\(\displaystyle 9x^2+30x+25\)

Explanation:

To multiply a difference squared, square the first term and add two times the multiplication of the two terms. Then add the second term squared.

\(\displaystyle (3x)^2+2(3x)(5)+(5)^2=9x^2+30x+25\)

Example Question #812 : Algebra

Which of the following is the square of \(\displaystyle 4x + 7y\) ?

Possible Answers:

\(\displaystyle 16x^{2}+ 56xy+ 49y^{2}\)

\(\displaystyle 16x^{2}+ 11xy+ 49y^{2}\)

\(\displaystyle 16x^{2}+ 28xy+ 49y^{2}\)

\(\displaystyle 16x^{2}+ 22xy+ 49y^{2}\)

\(\displaystyle 16x^{2} + 49y^{2}\)

Correct answer:

\(\displaystyle 16x^{2}+ 56xy+ 49y^{2}\)

Explanation:

Use the square of a sum pattern, substituting \(\displaystyle 4x\) for \(\displaystyle A\) and \(\displaystyle 7y\) for \(\displaystyle B\) in the pattern:

\(\displaystyle (A+ B)^{2}= A^{2}+ 2AB + B^{2}\)

\(\displaystyle (4x + 7y)^{2}= (4x)^{2}+ 2 (4x) (7y) + (7y)^{2}\)

\(\displaystyle = 16x^{2}+ 56xy + 49y^{2}\)

 

Example Question #1 : How To Find The Square Of A Sum

Which of the following is the square of \(\displaystyle 5 \sqrt{x} +3 \sqrt{y}\) ?

You may assume both \(\displaystyle x\) and \(\displaystyle y\) are positive.

Possible Answers:

\(\displaystyle 25x + 9y+ 30 \sqrt{xy}\)

\(\displaystyle 5x + 3y+ 15\sqrt{xy}\)

\(\displaystyle 25x + 9y+ 15\sqrt{xy}\)

\(\displaystyle 25x + 9y\)

\(\displaystyle 5x + 3y+ 30\sqrt{xy}\)

Correct answer:

\(\displaystyle 25x + 9y+ 30 \sqrt{xy}\)

Explanation:

Use the square of a sum pattern, substituting \(\displaystyle 5 \sqrt{x}\) for \(\displaystyle A\) and \(\displaystyle 3 \sqrt{y}\) for \(\displaystyle B\) in the pattern:

\(\displaystyle (A+ B)^{2}= A^{2}+ 2AB + B^{2}\)

\(\displaystyle (5 \sqrt{x}+3 \sqrt{y})^{2}= (5 \sqrt{x})^{2}+ 2 (5 \sqrt{x})\left (3 \sqrt{y} \right ) + \left (3 \sqrt{y} \right )^{2}\)

\(\displaystyle (5 \sqrt{x}+3 \sqrt{y})^{2}= 25x+ 30 \sqrt{xy} + 9y\)

or 

\(\displaystyle 25x + 9y+ 30 \sqrt{xy}\)

Example Question #121 : Exponents

Which of the following is the square of \(\displaystyle x^{2}+ x + 7\) ?

Possible Answers:

\(\displaystyle x^{4}+2x^{3}+15x^{2}+14x+49\)

\(\displaystyle x^{4}+ x^{2}+ 49\)

\(\displaystyle x^{4}+2x^{3}+8x^{2}+8x+49\)

\(\displaystyle x^{4}+ x^{3}+14x^{2}+7x+49\)

\(\displaystyle x^{4}+ x^{3}+14x^{2}+14x+49\)

Correct answer:

\(\displaystyle x^{4}+2x^{3}+15x^{2}+14x+49\)

Explanation:

Multiply vertically as follows:

                    \(\displaystyle \begin{matrix} x^{2}+ \; \; \; x +\; \; \; 7\\\underline{x^{2}+\; \; \; x +\; \; \; 7} \end{matrix}\)

                    \(\displaystyle 7 x^{2}+7 x +49\)

          \(\displaystyle x^{3}+ x^{2} + 7x\)

\(\displaystyle \underline{x^{4}+ x^{3}+7 x^{2} \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; }\)

\(\displaystyle x^{4}+2x^{3}+15x^{2}+14x+49\)

 

Example Question #7 : Squaring / Square Roots / Radicals

Which of the following is the square of \(\displaystyle y + \sqrt{17}\)  ?

Possible Answers:

\(\displaystyle y^{2}+ 34y+17\)

\(\displaystyle y^{2}+ y\sqrt{34}+17\)

The correct answer is not given among the other responses.

\(\displaystyle y^{2}+ 17y+17\)

\(\displaystyle y^{2}+ y\sqrt{17}+17\)

Correct answer:

The correct answer is not given among the other responses.

Explanation:

Use the square of a sum pattern, substituting \(\displaystyle y\) for \(\displaystyle A\) and \(\displaystyle \sqrt{17}\) for \(\displaystyle B\) in the pattern:

\(\displaystyle (A+ B)^{2}= A^{2}+ 2AB + B^{2}\)

\(\displaystyle (y + \sqrt{17})^{2}= y^{2}+ 2y \sqrt{17} + (\sqrt{17})^{2}\)

\(\displaystyle (y + \sqrt{17})^{2}= y^{2}+ 2y \sqrt{17} + 17\)

This is not equivalent to any of the given choices.

Example Question #2312 : Act Math

Which of the following is the square of \(\displaystyle \frac{1}{4}x + \frac{1}{7}\) ? 

Possible Answers:

\(\displaystyle \frac{1}{8}x ^{2}+ \frac{1}{28}x +\frac{1}{14}\)

\(\displaystyle \frac{1}{16}x ^{2}+ \frac{1}{56}x +\frac{1}{49}\)

\(\displaystyle \frac{1}{16}x ^{2}+ \frac{1}{28}x +\frac{1}{49}\)

\(\displaystyle \frac{1}{16}x ^{2}+ \frac{1}{14}x +\frac{1}{49}\)

\(\displaystyle \frac{1}{8}x ^{2}+ \frac{1}{14}x +\frac{1}{14}\)

Correct answer:

\(\displaystyle \frac{1}{16}x ^{2}+ \frac{1}{14}x +\frac{1}{49}\)

Explanation:

Use the square of a sum pattern, substituting \(\displaystyle 5 \sqrt{x}\) for \(\displaystyle A\) and \(\displaystyle 3 \sqrt{y}\) for \(\displaystyle B\) in the pattern:

\(\displaystyle (A+ B)^{2}= A^{2}+ 2AB + B^{2}\)

\(\displaystyle \left (\frac{1}{4}x + \frac{1}{7} \right )^{2}= \left (\frac{1}{4}x \right )^{2}+ 2 \left (\frac{1}{4}x \right )\left (\frac{1}{7} \right ) + \left (\frac{1}{7} \right )^{2}\)

\(\displaystyle = \frac{1}{16}x ^{2}+ \frac{1}{14}x +\frac{1}{49}\)

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