Precalculus : Find the Sum and Product of the Zeros of a Polynomial

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Find The Sum And Product Of The Zeros Of A Polynomial

Given \(\displaystyle y=5x^2+14x-3\), determine the sum and product of the zeros respectively.

Possible Answers:

\(\displaystyle \frac{7}{5},-\frac{21}{5}\)

\(\displaystyle \frac{14}{5},-\frac{3}{5}\)

\(\displaystyle \frac{1}{5},-3\)

\(\displaystyle \frac{16}{5}, -\frac{3}{5}\)

\(\displaystyle -\frac{14}{5},-\frac{3}{5}\)

Correct answer:

\(\displaystyle -\frac{14}{5},-\frac{3}{5}\)

Explanation:

To determine zeros of \(\displaystyle y=5x^2+14x-3\), factorize the polynomial.

\(\displaystyle 5x^2+14x-3=(5x-1)(x+3)\)

Set each of the factorized components equal to zero and solve for \(\displaystyle x\).

\(\displaystyle 5x-1=0\)

\(\displaystyle x=\frac{1}{5}\)

\(\displaystyle x+3=0\)

\(\displaystyle x=-3\)

The sum of the roots:

\(\displaystyle \frac{1}{5}+(-3)= \frac{1}{5}-\frac{15}{5}= -\frac{14}{5}\)

The product of the roots:

\(\displaystyle (\frac{1}{5})(-3)= -\frac{3}{5}\)

Example Question #431 : Pre Calculus

Please choose the best answer from the following choices.

 

Find the sum and product of the zeros of the following polynomial:
\(\displaystyle x^2-5x+6\)

Possible Answers:

\(\displaystyle Sum=1\)

\(\displaystyle Product=3/2\)

\(\displaystyle Sum=5\)

\(\displaystyle Product=6\)

\(\displaystyle Sum=1\)

\(\displaystyle Product=5\)

\(\displaystyle Sum=-5\)

\(\displaystyle Product=6\)

Correct answer:

\(\displaystyle Sum=5\)

\(\displaystyle Product=6\)

Explanation:

To find the zeros you have to factor the polynomial.

This is easily factorable and you will get \(\displaystyle (x-3)\) and \(\displaystyle (x-2)\).

Next, set both of these equal to zero. \(\displaystyle x-3=0\) and \(\displaystyle x-2=0\).

Isolate the x's and you will get \(\displaystyle x=3\) and \(\displaystyle x=2\).

The sum will be \(\displaystyle 5\) since you add the two together, and the product will be \(\displaystyle 6\) because you multiply the two together.

Example Question #1 : Find The Sum And Product Of The Zeros Of A Polynomial

Please choose the best answer from the following choices.

Find the sum and product of the zeros of the following polynomial:

\(\displaystyle 4x^2+15x+11\)

Possible Answers:

\(\displaystyle Sum=-15/4\)

\(\displaystyle Product=-11/4\)

\(\displaystyle Sum=-15/4\)

\(\displaystyle Product=11/4\)

\(\displaystyle Sum= -7/4\)

\(\displaystyle Product=11/4\)

\(\displaystyle Sum= 15/4\)

\(\displaystyle Product= 11/4\)

Correct answer:

\(\displaystyle Sum=-15/4\)

\(\displaystyle Product=11/4\)

Explanation:

Factoring the polynomial will give you \(\displaystyle (4x+11)\) and \(\displaystyle (x+1)\).

The zeros of these binomials will be \(\displaystyle x=-11/4\) and \(\displaystyle x=-1\).

If you add these together (sum) you get \(\displaystyle -15/4\) and if you multiply them together (product) you get \(\displaystyle 11/4\).

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