How do you find all the zeros of #f(x)=x^3+5x^2-4x-20#?
1 Answer
Jul 18, 2016
x = -5 , x = ± 2
Explanation:
The zeros of f(x) are the values of x that make f(x) = 0
solve:
#x^3+5x^2-4x-20=0# Begin by factorising the left side. Group the term in 'pairs'
#[x^3+5x^2]+[-4x-20]# and factorising each pair gives.
#x^2(x+5)-4(x+5)=(x+5)(x^2-4)#
#=(x+5)(x-2)(x+2)# Solving
#(x+5)(x-2)(x+2)=0# The zeros are
#x=-5,x=±2#
