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

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Answer 1 · 2015-05-12T02:29:51

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:
$x_1=3$
$x_2=-3$
$x_3=-1$

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