College Algebra : Zeros/Roots of a Polynomial

Study concepts, example questions & explanations for College Algebra

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Example Questions

Example Question #22 : Polynomial Functions

\(\displaystyle \begin{align*}&\text{Find the value(s) of x where the function: }f(x)=- 297x - 270x^{2} - 27\\&\text{crosses the x-axis.}\end{align*}\)

Possible Answers:

\(\displaystyle x=540,54\)

\(\displaystyle x=-540,-54\)

\(\displaystyle x=-1,-\frac{1}{10}\)

\(\displaystyle x=1,\frac{1}{10}\)

Correct answer:

\(\displaystyle x=-1,-\frac{1}{10}\)

Explanation:

\(\displaystyle \begin{align*}&\text{The function }f(x)=- 297x - 270x^{2} - 27\text{ crosses the x-axis}\\&\text{when it has a value of zero. To find the x values that}\\&\text{satisfy this, we can either factor the equation:}\\&-27\cdot (x + 1)\cdot (10x + 1)\\&\text{or, if this is not intuitive, use the quadratic formula:}\\&\frac{-b\pm\sqrt{b^2-4ac}}{2a}(\text{for equations of the form: }a^2x+bx+c)\\&\frac{-(-297)\pm\sqrt{(-297)^2-4(-270)(-27)}}{2(-270)}=\frac{297\pm243}{-540}\\&\text{Either way, we find that the function crosses the x-axis at}\ x=-1\text{ and }-\frac{1}{10}.\end{align*}\)

Example Question #1 : Zeros/Roots Of A Polynomial

\(\displaystyle \begin{align*}&\text{Find the value(s) of x where the function: }f(x)=- 822x - 288x^{2} - 567\\&\text{has a zero value.}\end{align*}\)

Possible Answers:

\(\displaystyle x=-\frac{7}{6},-\frac{27}{16}\)

\(\displaystyle x=-972,-672\)

\(\displaystyle x=972,672\)

\(\displaystyle x=\frac{7}{6},\frac{27}{16}\)

Correct answer:

\(\displaystyle x=-\frac{7}{6},-\frac{27}{16}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Given }f(x)=- 822x - 288x^{2} - 567\text{, to find when it has a value of}\\&\text{zero, we need a method to determine the x values that}\\&\text{make this happen. We can either factor the equation:}\\&-3\cdot (16x + 27)\cdot (6x + 7)\\&\text{or, if this is not intuitive, use the quadratic formula:}\\&\frac{-b\pm\sqrt{b^2-4ac}}{2a}(\text{for equations of the form: }a^2x+bx+c)\\&\frac{-(-822)\pm\sqrt{(-822)^2-4(-288)(-567)}}{2(-288)}=\frac{822\pm150}{-576}\\&\text{Either way, we find thatthe function crosses the x-axis at}\ x=-\frac{7}{6}\text{ and }-\frac{27}{16}.\end{align*}\)

Example Question #24 : Polynomial Functions

\(\displaystyle \begin{align*}&\text{Find the value(s) of x where the function: }f(x)=- 648x - 152x^{2} - 576\\&\text{crosses the x-axis.}\end{align*}\)

Possible Answers:

\(\displaystyle x=-3,-\frac{24}{19}\)

\(\displaystyle x=3,\frac{24}{19}\)

\(\displaystyle x=-912,-384\)

\(\displaystyle x=912,384\)

Correct answer:

\(\displaystyle x=-3,-\frac{24}{19}\)

Explanation:

\(\displaystyle \begin{align*}&\text{The function }f(x)=- 648x - 152x^{2} - 576\text{ crosses the x-axis}\\&\text{when it has a value of zero. To find the x values that}\\&\text{satisfy this, we can either factor the equation:}\\&-8\cdot (x + 3)\cdot (19x + 24)\\&\text{or, if this is not intuitive, use the quadratic formula:}\\&\frac{-b\pm\sqrt{b^2-4ac}}{2a}(\text{for equations of the form: }a^2x+bx+c)\\&\frac{-(-648)\pm\sqrt{(-648)^2-4(-152)(-576)}}{2(-152)}=\frac{648\pm264}{-304}\\&\text{Either way, we find thatthe function crosses the x-axis at} \ x=-3\text{ and }-\frac{24}{19}.\end{align*}\)

Example Question #2 : Zeros/Roots Of A Polynomial

\(\displaystyle \begin{align*}&\text{Find the value(s) of x where the function: }f(x)=712x - 110x^{2} - 728\\&\text{crosses the x-axis.}\end{align*}\)

Possible Answers:

\(\displaystyle x=-280,-1144\)

\(\displaystyle x=280,1144\)

\(\displaystyle x=\frac{26}{5},\frac{14}{11}\)

\(\displaystyle x=-\frac{26}{5},-\frac{14}{11}\)

Correct answer:

\(\displaystyle x=\frac{26}{5},\frac{14}{11}\)

Explanation:

\(\displaystyle \begin{align*}&\text{The function }f(x)=712x - 110x^{2} - 728\text{ crosses the x-axis}\\&\text{when it has a value of zero. To find the x values that}\\&\text{satisfy this, we can either factor the equation:}\\&-2\cdot (11x - 14)\cdot (5x - 26)\\&\text{or, if this is not intuitive, use the quadratic formula:}\\&\frac{-b\pm\sqrt{b^2-4ac}}{2a}(\text{for equations of the form: }a^2x+bx+c)\\&\frac{-(712)\pm\sqrt{(712)^2-4(-110)(-728)}}{2(-110)}=\frac{-712\pm432}{-220}\\&\text{Either way, we find thatthe function crosses the x-axis at}\ x=\frac{26}{5}\text{ and }\frac{14}{11}.\end{align*}\)

Example Question #3 : Zeros/Roots Of A Polynomial

\(\displaystyle \begin{align*}&\text{Find the value(s) of x where the function: }f(x)=- 544x - 152x^{2} - 480\\&\text{crosses the x-axis.}\end{align*}\)

Possible Answers:

\(\displaystyle x=-2,-\frac{30}{19}\)

\(\displaystyle x=2,\frac{30}{19}\)

\(\displaystyle x=608,480\)

\(\displaystyle x=-608,-480\)

Correct answer:

\(\displaystyle x=-2,-\frac{30}{19}\)

Explanation:

\(\displaystyle \begin{align*}&\text{The function }f(x)=- 544x - 152x^{2} - 480\text{ crosses the x-axis}\\&\text{when it has a value of zero. To find the x values that}\\&\text{satisfy this, we can either factor the equation:}\\&-8\cdot (x + 2)\cdot (19x + 30)\\&\text{or, if this is not intuitive, use the quadratic formula:}\\&\frac{-b\pm\sqrt{b^2-4ac}}{2a}(\text{for equations of the form: }a^2x+bx+c)\\&\frac{-(-544)\pm\sqrt{(-544)^2-4(-152)(-480)}}{2(-152)}=\frac{544\pm64}{-304}\\&\text{Either way, we find thatthe function crosses the x-axis at}\ x=-2\text{ and }-\frac{30}{19}.\end{align*}\)

Example Question #27 : Polynomial Functions

\(\displaystyle \begin{align*}&\text{Find the value(s) of x where the function: }f(x)=225x^{2} - 623x + 374\\&\text{crosses the x-axis.}\end{align*}\)

Possible Answers:

\(\displaystyle x=\frac{22}{25},\frac{17}{9}\)

\(\displaystyle x=-850,-396\)

\(\displaystyle x=-\frac{22}{25},-\frac{17}{9}\)

\(\displaystyle x=850,396\)

Correct answer:

\(\displaystyle x=\frac{22}{25},\frac{17}{9}\)

Explanation:

\(\displaystyle \begin{align*}&\text{The function }f(x)=225x^{2} - 623x + 374\text{ crosses the x-axis}\\&\text{when it has a value of zero. To find the x values that}\\&\text{satisfy this, we can either factor the equation:}\\&(25x - 22)\cdot (9x - 17)\\&\text{or, if this is not intuitive, use the quadratic formula:}\\&\frac{-b\pm\sqrt{b^2-4ac}}{2a}(\text{for equations of the form: }a^2x+bx+c)\\&\frac{-(-623)\pm\sqrt{(-623)^2-4(225)(374)}}{2(225)}=\frac{623\pm227}{450}\\&\text{Either way, we find thatthe function crosses the x-axis at}\ x=\frac{22}{25}\text{ and }\frac{17}{9}.\end{align*}\)

Example Question #4 : Zeros/Roots Of A Polynomial

\(\displaystyle \begin{align*}&\text{Find the value(s) of x where the function: }f(x)=108x^{2} - 60x - 25\\&\text{has a zero value.}\end{align*}\)

Possible Answers:

\(\displaystyle x=180,-60\)

\(\displaystyle x=\frac{5}{6},-\frac{5}{18}\)

\(\displaystyle x=-\frac{5}{6},\frac{5}{18}\)

\(\displaystyle x=-\frac{5}{6},-\frac{5}{18}\)

Correct answer:

\(\displaystyle x=\frac{5}{6},-\frac{5}{18}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Given }f(x)=108x^{2} - 60x - 25\text{, to find when it has a value of}\\&\text{zero, we need a method to determine the x values that}\\&\text{make this happen. We can either factor the equation:}\\&(18x + 5)\cdot (6x - 5)\\&\text{or, if this is not intuitive, use the quadratic formula:}\\&\frac{-b\pm\sqrt{b^2-4ac}}{2a}(\text{for equations of the form: }a^2x+bx+c)\\&\frac{-(-60)\pm\sqrt{(-60)^2-4(108)(-25)}}{2(108)}=\frac{60\pm120}{216}\\&\text{Either way, we find thatthe function crosses the x-axis at}\ x=\frac{5}{6}\text{ and }-\frac{5}{18}.\end{align*}\)

Example Question #5 : Zeros/Roots Of A Polynomial

\(\displaystyle \begin{align*}&\text{Find the value(s) of x where the function: }f(x)=421x + 306x^{2} - 210\\&\text{has a zero value.}\end{align*}\)

Possible Answers:

\(\displaystyle x=238,-1080\)

\(\displaystyle x=-238,1080\)

\(\displaystyle x=\frac{7}{18},-\frac{30}{17}\)

\(\displaystyle x=-\frac{7}{18},\frac{30}{17}\)

Correct answer:

\(\displaystyle x=\frac{7}{18},-\frac{30}{17}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Given }f(x)=421x + 306x^{2} - 210\text{, to find when it has a value of}\\&\text{zero, we need a method to determine the x values that}\\&\text{make this happen. We can either factor the equation:}\\&(17x + 30)\cdot (18x - 7)\\&\text{or, if this is not intuitive, use the quadratic formula:}\\&\frac{-b\pm\sqrt{b^2-4ac}}{2a}(\text{for equations of the form: }a^2x+bx+c)\\&\frac{-(421)\pm\sqrt{(421)^2-4(306)(-210)}}{2(306)}=\frac{-421\pm659}{612}\\&\text{Either way, we find thatthe function crosses the x-axis at} \ x=\frac{7}{18}\text{ and }-\frac{30}{17}.\end{align*}\)

Example Question #6 : Zeros/Roots Of A Polynomial

\(\displaystyle \begin{align*}&\text{Find the value(s) of x where the function: }f(x)=323x + 29x^{2} - 300\\&\text{has a zero value.}\end{align*}\)

Possible Answers:

\(\displaystyle x=-12,\frac{25}{29}\)

\(\displaystyle x=12,-\frac{25}{29}\)

\(\displaystyle x=-50,696\)

\(\displaystyle x=50,-696\)

Correct answer:

\(\displaystyle x=-12,\frac{25}{29}\)

Explanation:

\(\displaystyle \begin{align*}&\text{Given }f(x)=323x + 29x^{2} - 300\text{, to find when it has a value of}\\&\text{zero, we need a method to determine the x values that}\\&\text{make this happen. We can either factor the equation:}\\&(x + 12)\cdot (29x - 25)\\&\text{or, if this is not intuitive, use the quadratic formula:}\\&\frac{-b\pm\sqrt{b^2-4ac}}{2a}(\text{for equations of the form: }a^2x+bx+c)\\&\frac{-(323)\pm\sqrt{(323)^2-4(29)(-300)}}{2(29)}=\frac{-323\pm373}{58}\\&\text{Either way, we find thatthe function crosses the x-axis at}\ x=-12\text{ and }\frac{25}{29}.\end{align*}\)

Example Question #7 : Zeros/Roots Of A Polynomial

\(\displaystyle \begin{align*}&\text{Find the root(s) the function: }f(x)=379x + 276x^{2} - 696\end{align*}\)

Possible Answers:

\(\displaystyle x=\frac{24}{23},-\frac{29}{12}\)

\(\displaystyle x=576,-1334\)

\(\displaystyle x=-\frac{24}{23},\frac{29}{12}\)

\(\displaystyle x=-576,1334\)

Correct answer:

\(\displaystyle x=\frac{24}{23},-\frac{29}{12}\)

Explanation:

\(\displaystyle \begin{align*}&\text{The roots of the function }f(x)=379x + 276x^{2} - 696\text{ are the x values}\\&\text{that give it a value of zero. To find these x values}\\&\text{we can either factor the equation:}\\&(12x + 29)\cdot (23x - 24)\\&\text{or, if this is not intuitive, use the quadratic formula:}\\&\frac{-b\pm\sqrt{b^2-4ac}}{2a}(\text{for equations of the form: }a^2x+bx+c)\\&\frac{-(379)\pm\sqrt{(379)^2-4(276)(-696)}}{2(276)}=\frac{-379\pm955}{552}\\&\text{Either way, we find thatthe function crosses the x-axis at}\ x=\frac{24}{23}\text{ and }-\frac{29}{12}.\end{align*}\)

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