```
````f(x) = (x + 3)(x - 5)`

Then `x = -3`

and `x = 5`

make `f(x)`

zero.

The above answer was easy because `f(x)`

was factored.
The answer is less obvious for

```
````f(x) = x`^{2} - 2x - 15

Of course, in general, the coefficients are not integers, which makes the problem even more difficult (unless you have a calculator):

```
````g(x) = 4.592x`^{2} + 2.308x - 8.083

Fortunately, the quadratic formula provides a way to find the roots. If the quadratic is

```
````ax`^{2} + bx + c

then the formula gives your the roots, if any.

(Math Review:) Will there be two roots for every choice of `a`

, `b`

, and `c`

?