Given the polynomial f(x)=21x5−6x3+8x+9
What one of the following is a possible rational root?
Select one:
a. 8 / 4
b. 5 / 8
c. 7 / 8
d. 3 / 7

Question

Given the polynomial f(x)=21x5−6x3+8x+9
What one of the following is a possible rational root?  
Select one:
a. 8 / 4
b. 5 / 8
c. 7 / 8
d. 3 / 7

directrix · Answer

Read about the theorem here; http://www.mathwords.com/r/rational_root_theorem.htm

directrix · Answer

The contenders for rational roots are form, in this case, by rational numbers whose numerators are factors of 9 and whose denominators are factors of 21.

directrix · Answer

Looking at the answer options, a. 8 / 4 could not be a rational root for this polynomial because 8 is not a factor of 9 and 4 is not a factor of 21. Discard that option.

directrix · Answer

You can discard this option for the same reason: b. 5 / 8

I leave it to you to examine the remaining two options. One of them is the answer.

@fabulous98