Can you make a rectangle out of two triangles and a square?

Sure, place a triangle's hypotenuse (longest side) on the other triangle's hypotenuse, that will give either a square or a rectangle. Then place the square on one end of the rectangle.

For this to work though, the length of the square's side HAS to equal the length of the triangles hypotenuses, and likewise each triangle's hypotenuse much equal the length of a side of the square.

Hope this is clear.