# How do you find the intervals of increasing and decreasing using the first derivative given #y=x^2-2x-8#?

##### 1 Answer

Mar 30, 2017

See below

#### Explanation:

The first derivative should return the **slope** of the function, or to be more precise **the equation that allows you to compute the slope of the function** .

We have:

In this case, the first derivative is:

If we want a **zero slope** , we say that:

For a **positive** slope, so that

So the **interval** is:

And for a **negative** slope, so that **decreasing** as we move left - right along the x axis, we say that:

So the **interval** is:

We can plot it as well: