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Find the sum to n terms of the series :5...

Find the sum to n terms of the series :`5^2+6^2+7^2+dotdotdot+20^2`

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The correct Answer is:
N/a
`5^(2) + 6^(2) + 7^(2) + … + 20^(2)`
`=(1^(2) + 2^(2) + 3^(2) + 4^(2) + 5^(2) + … + 20^(2))`
`-(1^(2) + 2^(2) + 3^(2) + 4^(2))`
`= sum(20)^(2) - sum(4)^(2)`
`= (1)/(6) (20) (20 +1) [2(20) + 1]`
`- (1)/(6) (4) (4 +1) [2(4) + 1]`
`= (1)/(6)(420)(41) - (1)/(6)(20) (9)`
= 2870 - 30 = 2840.
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