under the angle menu, look at #7 and #8 items ...
7. syntax is ... P "arrow" Rx(r, theta)
where r is the ray length and theta is the ray angle relative to the x-axis. output is the x-coordinate.
8. syntax is ... P "arrow" Ry(r, theta)
output is the y-coordinate.
items #5 and #6 under the same menu convert rectangular to polar ... input is R "arrow" Pr(x,y) and R "arrow" P theta (x,y) respectively; output is r for #5 and theta for #6.
don't forget to check the mode switch for the correct form for angles you're using, degrees or radians.