Question

How do you find all zeros of `y=x^3+x^2-9x-9`?

Answer 1

Set `y=0` and solve for `x`:
`x^3+x^2-9x-9=0`

Collecting `x` from the first and third term:
`x(x^2-9)+x^2-9=0`
`(x^2-9)(x+1)=0`
So:

`x^2-9=0`
`x=+-sqrt(9)=+-3`
and

`x+1=0`

Giving:
`x_1=3`
`x_2=-3`
`x_3=-1`