need to have a math equation that finds the length of the segment of line that is located between 2 points on that line.

The variables I know are:

1. x, y of one point

2. x, y of other point

3. angle of the line (it can rotate anywhere in 360 degrees, its rotation point is the second point)

I'm just a programmer who isn't that good at math

Thanks in advance! Ask if you have any questions!

And here's the pic of the math problem for some visual:

EDIT: Oops, never mind about the Radius of the circle, that wont help.