find all zeroes

Question

Find all zeros of the function f(x) = x^3 – 5x 2 – 4x + 20. Give exact values, not decimal approximations

Answer 1

f(x) = x³ – 5x² – 4x + 20

f(x)= [x² (x-5)] - [4(x-5)]

f(x)= (x²-4) (x-5)

f(x) = (x+2)(x-2)(x-5)

x= +2, -2, +5