Say we are given the Cartesian points P1=(x1, y1) and P2=(x2, y2).

P1-------------------P3-----------------------------------P2

|----------m--------| |----------------n-------------------|

We want to find the coordinates of P3. Use this formula:

Now what if the points were in polar: P1=(r1, theta1) and P2=(r2, theta2). What is the equivalent equation for polar coordinates?