Prove that the circles described on the four sides of a rhombus as diameters, pass through the point of intersection of its diagonals.
Let ABCD be a rhombus such that its diagonals AC and BD intersects at O
Since, the diagonals of a rhombus intersect at right angle
Therefore,
∠ACB = ∠BOC = ∠COD = ∠DOA = 90o
Now,
∠AOB = 90o = circle described on AB as diameter will pass through O
Similarly, all the circles described on BC, AD and CD as diameter pass through O.