Question 1000381
Here are some hints. You can do this problem once you have them.

The diagonal is the circle's diameter. You are given the circle's radius, so you know the length of the diameter.

According to Thale's theorem any triangle that has three points on a circle and include one side that is a diameter, must be a right triangle.

You know the length of two sides of two different right triangles. Use that information to find the third side of both triangles. 

Then find the area of each triangle using Herons Formula.