Question 38023
f(x)=x^3+x^2-5x-6 has a zero at x=-2

Use your long division.
Divide f(x) by x+2 and you will get a 
quotient of x^2-x-3 and with a remainder
of zero.
Now solve the quotient for x by using the
quadratic formula, as follows:
x=[1+sqrt(1+12)]/2=[1+-sqrt(13)]/2
This means the other two factors are:
(x-[(1/2)+(1/2)sqrt13]) and (x-[(1/2)-(1/2)sqrt13])
Cheers,
Stan H.