to find the angle formed by the ground and the hypotenuse, you calculate the inverse tangent of (50 / 40), 51.53 degrees. (remember, sohcahtoa)

Since a triangle has 180 degrees and the angle made by the ground and the tree is 90 degrees, the angle made by the tree and the hypotenuse is 180 - (90 + 51.54), which is 38.66 degrees. I'd be happy to go into more detail if you'd like.

You could also calculate the inverse tangent of (40/50). In this case, you would be dealing directly with the angle formed by the tree and the hypotenuse.