I won't do yours for you.  I'll do one exactly like it instead
and you can use it as a model to do yours by.  I'll do this
one instead which uses cosine instead of sine:



Always draw this picture when converting from polar to ractangular 
or from rectangular to polar::



Looking at the triangle in the picture above you can see these:

, , 

Then solve for y, x and r

, ,  {r=sqrt(x^2+y^2)}}}

ALWAYS WAIT TILL LAST TO SUBSTITUTE FOR r. Substitute for x and y
first. Then simplify.





Multiply through by r



NOW, FINALLY, we substitute for r2.

   <-- answer

That's it!.

Now do yours the same way, only use the sine instead.

Edwin