Math, asked by hardikverma360, 1 year ago

evaluate 5^2 + 6^2 + 7^2 + ....... + 20 ^ 2 .plzz Solve this

Answers

Answered by Anonymous
1

Answer:

2840

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Step-by-step explanation:

Useful formula:

1² + 2² + 3² + ... + n² = n ( n + 1 ) ( 2n + 1 ) / 6

So

5² + 6² + ... + 20²

= ( 1² + 2² + ... + 20² ) - ( 1² + 2² + 3² + 4² )

= 20 × 21 × 41 / 6  -  4 × 5 × 9 / 6

= 10 × 7 × 41  -  2 × 5 × 3

= 2870 - 30

= 2840

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