Question
(`11^2` + `12^2` + `13^2` +...........+ `20^2` ) = ?
Answer: Option B
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(`11^2` + `12^2` + `13^2` +...........+ `20^2` )
=(`1^2` + `2^2` + ...........+ `20^2` ) - (`1^2` + `2^2` + ..........+ `10^2` )
=` { (20 xx 21 xx 41)/(6)` - ` (10 xx 11 xx 21)/(6)}`
`because ` [ (` 1^2` + `2^2` + ........+`n^2`) = `1/6` n(n + 1)(2n + 1)]
= (2870 - 385) = 2485
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