ABC and ADC are two right triangles with common hypotenuse AC. Prove that .
From figure, it is clear that,
, which means
These angles are in the semicircle.
Therefore both triangles and are lying in the semicircle.
AC is the diameter of circle with center O.
Therefore, Points A, B, C and D are concyclic means all the points lie on the circle.
Thus, CD is a chord.
Therefore, (Angles in the same segment of the circle)