[list=1][*]Use Semi-Circle Through 2 Points (6th menu) to add a semi-circle to the screen end-points A and B.[br][br][/*][*]Use Point (2nd menu) to add a new point on the circle, C.[br][br][/*][*]Use Segment (3rd menu) to create segments AB, AC and BC.[br][br][/*][*]Use the Angle tool (8th menu) to measure the angle ACB.[br][/*][/list]