When converting between rectangular and polar form,
either to or from, always draw this first:
Then write down the trig functions for the triangle:
Since we are converting from rectangular to polar, we solve
each of those for x and y.
[If we were converting from polar to rectangular, we would
solve each for r.]
Substitute for x and y:
Simplify and if reasonably easy, solve for r or rē:
We can even make it simpler by substituting
for 
Edwin
