AB and CD are diameters of one circle. Prove that AC || BD and find the angle ABC if the angle BD = 44 degrees.

Let’s connect the ADВС points into a quadrangle. In the formed quadrangle ADВС, the diagonals AB and DС are the diameters of the circle, which at the point of intersection O are halved and equal to each other.
If in a quadrangle the diagonals are equal and at the point of intersection they are divided in half, then this is either a square or a rectangle. Since the ВAD angle is 440, the ADВС is a rectangle. Then the AС is parallel to the ВD, which was required to be proved.
The angle ABC is equal to the angle ABC as the cross-lying angles at the intersection of parallel ABP and BC secant AB, then the angle ABC is 44.
Answer: Angle ABC is 440.