ABC is a right-angled triangle and O is the mid point of the side opposite to the right angle. Explain why O is equidistant from A, B, and C. (The dotted lines are drawn additionally to help you)

ABCD is a rectangle as opposite sides are equal and parallel to each other and interior angles are of 90°. AD=BC, and AB=DC. In rectangle, diagonals are of equal length and also these bisect each other. AC=BD. 1/2AC=1/2BD. ∴OA=OC=OB=OD. so, OA=OC=OD, which means O point is at equal distant from A,B,C. hence, O is equidistant from A, B, and C.