Hello

Quesiton:

Find the rectangular form of the equation of the tangent line to the polar curve $\displaystyle r=cos^3(\theta)$ at the point corresponding to $\displaystyle \theta=\frac{\pi}{4}$

How to do that?

I mean finding it inRECTANGULAR FORM!

i know that $\displaystyle \frac{dy}{dx}=\frac{\frac{dr}{d\theta} sin(\theta)+rcos(\theta)}{\frac{dr}{d\theta} cos(\theta) - r sin(\theta)}$

I will calculate $\displaystyle \frac{dy}{dx}$ at $\displaystyle \theta=\frac{\pi}{4}$ , and this is easy ..

The problem here is that, how can I find the equation of the tangent line inRECATNGULAR FORM??

The equation of the tangent line is :

$\displaystyle y-y1=m(x-x1)$

m = the slope , and this one will be calculated by using the formula ..

but what about x1 and y1?