Originally Posted by

**sleigh** Hi. I was taking a practice test for a Math Contest and I can not figure out what the answer to one question is. Here is the question:

The function $\displaystyle f(x)=x^3+7x^2-6x+72 $has roots $\displaystyle r1 , r2 , r3$ (i.e. $\displaystyle f(r1)=f(r2)=f(r3)=0$). Find $\displaystyle r1+r2+r3$.

A. 7

B. -7

C. 0

D. -5

E. None of these.

Correct answer: B

I used the zeros function on the TI 89, and it said that the only zero of the function was -8.65..., so I put E, but I don't see why this is wrong. Could someone explain this question to me? Thanks!