# What is the slope of the tangent line of #(x-y)(x+y)-xy+y= C #, where C is an arbitrary constant, at #(1,2)#?

##### 1 Answer

Feb 2, 2016

The slope of the tangent is

#### Explanation:

Instead of differentiating immediately, let's rewrite the first product.

This form is (I think) simpler to differentiate.

At the point

Solve for