# How do you solve #y=x^3 + 3x^2 - 6x # using the quadratic formula?

##### 1 Answer

#### Answer:

This cubic has 3 roots:

We can solve it be dividing through by

#### Explanation:

This is not a quadratic, it's a cubic, so it'll have 1-3 roots rather than 0-2 (think about the shape of a cubic compared to a parabola-shaped quadratic and how each can cut the x-axis).

It's a tricky one, but we can divide through by x and treat it as:

One root of this will be

The other roots will be when the parenthesis is equal to

And hey presto, we have a quadratic to solve! And we know how to do that: the quadratic formula. For a quadratic in the form:

We know:

Therefore

Remember that we had the other root,