One student reported to the teacher that he had discovered "that a triangle equals a square." When the teacher asked him to explain, the student went to the block corner and took two half-unit (square) blocks, two half-unit triangular (triangle) blocks, and one unit (rectangle) block (shown in fig. 4.29). He said, "If these two [square half-units] are the same as this one unit and these two [triangular half-units] are the same as this one unit, then this square has to be the same as this triangle!