Okay, well I have 2 fingers on an iPhone. The finger higher up will be called, "finger 2", where-as the finger lower down will be known as, "finger 1". Now suppose I were to take the x value of finger 2 along with the y value of finger 1 and create a third point called, "point 3" I would now have 3 points and an imaginary if you well, right triangle.

I want to find the angle of the intersection of line segment (point 3, finger 1) and line segment (finger 1, finger 2)... I want to find the angle of the intersection at the point, finger 1.

Also it needs to be in radians. What do I do to solve this, it has been ages since I've done trigonometry.

Diagram attached: .

In your equations to make things simpler we will define the following variables:

X1 = The x-value of finger 1.

Y1 = The y-value of finger 1.

X2 = The x-value of finger 2.

Y2 = The y-value of finger 2.

X3 = The x-value of point 3.

Y3 = The y-value of point 3.

Angle1 = The angle we are solving for.

Thank-you very much!