You can download the template here and cut it out or make it on card. Try the puzzle yourself.
Either make a square with 5 pieces or make a square with 6 pieces.
If you don’t have a printer, here are instructions for drawing your own squares and triangles and making your own jigsaw pieces. If you do this you can choose any right angled triangle whatsoever and then make your jigsaw using that triangle.
The third challenge is to explain this.