Answer: x³-21x+20=0
Step-by-step explanation:
To find which polynomial has 1, 4, -5 as the roots, all we have to do is equal each root to 0 and multiply all factors together.
1 is (x-1)=0
4 is (x-4)=0
-5 is (x+5)=0
Now, we just multiply them together.
(x-1)(x-4)(x+5)=0 [FOIL]
(x²-4x-x+4)(x+5)=0 [combine like terms]
(x²-5x+4)(x+5)=0 [FOIL]
x³+5x²-5x²-25x+4x+20=0 [combine like terms]
x³-21x+20=0
Now we know x³-21x+20=0 is the polynomial with those roots.
