Polar/Rectangular Coordinates

If given only the polar coordinates (r,Ѳ), how could you find the rectangular coordinates (x,y)? Verify this using calculations and by using the applet. If given only the rectangular coordinates (x,y), how could you find the polar coordinates (r,Ѳ)? Verify this using calculations and by using the applet. Positioning point A in any quadrant, why is the polar coordinate r in (r,Ѳ) always positive?