the expression

f(x) = x^3 + ax^2 + bx + 10

is divisible by (x+2) but leaves a remainder of 12 when divided by (x+1)

a) Find the values of a and b

b) solve the equation f(x) = 0

i have done a) (i think) and come up with a = 4 b = -7 (is that right)

and im completely stumped on b)

any help is appericated