# What is the equation of the tangent line of #r=cos(theta+pi/2)*cos(theta-pi) # at #theta=(-pi)/8#?

##### 1 Answer

Simplify before you differentiate.

#### Explanation:

By the Cosine Sum Formula

By the Cosine Difference Formula

Their product is

By the Sine Double angle formula, we have

To find the slope of the tangent line, use the fact that

Finally, determine the point (x, y) corresponding to the point that you are interested in, where