# What is the first derivative and critical numbers of #y= (x^4)/(x^4-1)#?

##### 1 Answer

Critical points are at

#### Explanation:

This derivative can of course be computed by using the quotient rule. However, that tends to be somewhat cumbersome, so we can be clever. If we use a bit of algebraic long division, we can get away with a simple chain rule application.

Let

Resubstitute:

To solve for the critical points, we simply set the derivative expression equal to 0 and solve for x, and also find any x's where the function is undefined:

When we have an expression of something divided by something else equals 0, we can deduce that the top expression must be 0, since if the bottom were to be 0, the value would be undefined.

So, we know that

So, if