\( 120 = \frac{n}{2}(2×4 + (n−1)×4) = \frac{n}{2}(8 + 4n − 4) = \frac{n}{2}(4n + 4) = 2n(n + 1) \)

Fri, 17 Apr 2026 18:25:07 +0000

Content under review