It is really important that you start to realize patterns when you are dealing with right triangles. As you change the triangle (move vertex F), I want you to not only pay attention to the fact that one angle will always remain 90 degrees but I want you pay extra attention to the sum of the other two angles. What do you notice when you add the other two angles of a right triangle together?
Assume a right triangle has an angle of 50 degrees. What is the measure of the other angle?