Finding an angle with 3 CGPoints

Question

In my application, a user taps 3 times and an angle will be created by the 3 points that were tapped. It draws the angle perfectly. I am trying to calculate the angle at the

Answer 1

Using this answer to compute angle of the vector:

CGFloat angleForVector(CGFloat dx, CGFloat dy) {
    return atan2(dx, -dy) * 180.0/M_PI;
}

// Compute angle at point Corner, that is between AC and BC:

CGFloat angle = angleForVector(A.x - Corner.x, A.y - Corner.y)
              - angleForVector(B.x - Corner.x, B.y - Corner.y);

NSLog(@"FULL ANGLE IS: %f, ANGLE IS: %.2f",angle, angle);