1² + 2² + 3² + 4² + ........... + 20² = কত?

প্রশ্ন: 1² + 2² + 3² + 4² + ........... + 20² = কত?

সমাধান:
আমরা জানি,
1² + 2² + 3² + 4² + ........... + n² = (1/6){n(n+1)(2n + 1)}

1² + 2² + 3² + 4² + ........... + 20² = (1/6){20(20+1)(2×20 + 1)}
= (20×21×41)/6
= 2870