Question

The function f ( x ) = x ^3 + 2x^2− 5 x − 6 has a root at 2. Name all roots of this function.

a.-2, -1, -3


b.2, 1, 3


c.2, -1, -3


d.-2, 1, 3

Answer 1

sub x=1 into f(x),

remainder= 1^3+2(1)^2-5(1)-6= -8

since remainder≠0, x=1 is not a root of the function

sub x=-1,

remainder = (-1)^3+2(-1)^2-5(-1)-6= 0

by remainder theorem,

x=-1 is a root of f(x)

hence, the correct ans is c