Proof for Euler's Theorem

I'd like a proof for Euler's theorem that can be understood by a high school student.

Total area of a triangle

A 1 acre field in the shape of a right triangle has a post at the midpoint of each side. A sheep is tethered to each of the side of the post on the hypotenuse. The ropes are just long enough to let each animal reach the two adjacent vertices. What is the total area the two sheep have to themselves?

A 1 acre area field in the shape of a right triangle has a post at the midpoint of each side

A 1 acre area field in the shape of a right triangle has a post at the midpoint of each side. A sheep is tethered to each side posts and a goat to the post in the hypotenuse. The ropes are just long enough to let each animal reach the two adjacent vertices. What is thw total area the two sheep have to themselves? i.e. the area the goat can' reach.

determining the distance

Joe and jill set sail from the same point, with Joe sailing in the direction of S4degree east and Jill sailing in the direction S9degree west. After 4 hr, Jill 2 mi due west of Joe. How far had jill sailed?

Understanding solid figures.

What are solid figures?