By placing the pinwheel on top of the original square, students will see that they have the same area. By inspection, students should notice that the four uncovered triangles on the square are congruent to the four green triangles that extend beyond the sides of the square. Alternatively, students can decompose the pinwheel into an interior octagon and eight parallelograms and calculate the area of each; the sum of those areas will equal the area of the original square.