SOLUTION: Hello, I need help with this problem: Find all rational roots of the equation x^3-5x^2-4x+20=0 and then find the irrational roots if there are any? Thank you.

Algebra ->  Rational-functions -> SOLUTION: Hello, I need help with this problem: Find all rational roots of the equation x^3-5x^2-4x+20=0 and then find the irrational roots if there are any? Thank you.      Log On


   

Question 448579: Hello,
I need help with this problem:
Find all rational roots of the equation x^3-5x^2-4x+20=0
and then find the irrational roots if there are any?
Thank you.
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

Find all rational roots of the equation 

 x^3-5x^2-4x+20=0   |If x = 2  then 8-20-8-20= 0

 x^3-5x^2-4x+20)/(x-2) = x^2-3x-10

 (x-2)(x^2-3x-10) = 0

           x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+ 

           x+=+%283+%2B-+sqrt%28+49+%29%29%2F%282%29+ 

              x = (3 ± 7)/2   x = 5 and x = -2

 Rational roots are: -2,2,5