, , ≠ 0 + 2 2 + 3 − 2 2 2 2 + 2 2 + 3 − 2 2 2 2 = 2 2−1 = 2 = 1 1 2 2 + 2 2 + 3 − 2 2 + 2 2 + 3 − 2 = 2 × ( + 1) 2 = (2 × ) + (2 × 1) 2 2 2 + = 2 + − 2 2 − + 2 2 + 3 − 2 = × 1−1 = × = × 1 = 2 0 2 2 + − 2