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 : Descartes' Rule, Intermediate Value Theorem, Sum And Product Of Zeros

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{1}{5},-3

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

\displaystyle -\frac{14}{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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