I have my own proof of this . . .Code:A o * * r * @ * * * O * o * * 2@* r * @ * r * * * * C o * * * o B
Right triangle can be inscribed in a semicircle.
. . is the center of the circle
. . and are radii of the circle.
Hence, is isosceles and
is an exterior angle of .
. . Hence: .