Question

Which of the following is a rational zero of the function

P(x)= 4x^4 + 8x^3 -7x^2 -21x-9

A. -3/2
B. -1
C. -3/4

And please explain!!!

Answer 1

-3/2

Explanation:

Just took test on odyssey

Answer 2

Applying the rational roots theorem because of the -9 and 4, -3/2 looks like a good bet because -3 is a factor of -9 and 2 is a factor of 4.

Plugging x = -3/2 into the function we have

4(-3/2)^4 + 8(-3/2)^3 - 7(-3/2)^2 - 21(-1.5) - 9 = 0

so -3/2 is a zero

x = 1 and x = -3/4 are not zeroes.