Complete the steps to solve the polynomial equation x3-21x=-20 according to the rational root theorem, which number is a potential root of the polynomial?

X^3 - 21x + 20 = 0

potential roots are factors of 20    eg 1, 2 ,4 ,5, 10, 20  and the negative values of these
1 looks like a rots . Try it:-
f(1) = 1 - 21 + 20 = -20+20 = 0

Yes  1 is  a solution.

2 is not.

Try 4:-

4^3 - 21*4 + 20  =  64 - 84 + 20  = 0 

Try 5   No 
Try 10 - N0 
20 no.

Try -4  - No
-5:-

Yes  

Roots are  1, 4 and -5

Ithink if im not mistaking b is -3 but im not a 100% sude