Let A B C be a right triangle with \angle B C A=90^{\circ}. A circle with diameter A C intersects the hypotenuse A B at K. If B K: A K=1: 3, find the measure of the angle \angle B A C.
Let A B C be a right triangle with \angle B C A=90^{\circ}. A circle with diameter A C intersects the hypotenuse A B at K. If B K: A K=1: 3, find the measure of the angle \angle B A C.