You can see one angle labelled 40º. This means the triangle cannot be equilateral, because each angle would need to be 60º. You can see that two of the sides are equal.

Learn about properties of triangles with this BBC Bitesize Maths article. For students between the ages of 11 and 14.

For starters, the triangle and square must have equal areas because the pieces are the same. For a square, its longest possible cut is across the diagonal.