What sort of a quadrilateral is formed by the tangents at the ends of two perpendicular diameters of a circle?

Prove that the tangents drawn to a circle at the two ends of a diameter are parallel.

In the picture a triangle is formed by two mutually perpendicular tangents to a circle and a third tangent. Prove that the perimeter of the triangle is equal to the diameter of the circle.

The picture shows two circles with the same centre and two triangles formed by joining the centre to the points of intersection of the circles with two radii of the larger circle. prove that these triangles are similar .