Question

5^2 +6^2+7^2+....+20^2. ​

Answer 1

Step-by-step explanation:

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Answer 2

Question:-

Find the sum to n terms of the series 5²+6²+7²+...+20²

Answer:

2840

5²+6²+7²+...+20²

=(1²+2²+...+20²)−(1²+2+3+4²)

sum of square is n(n+1)(2n+1)/6

for n = 20

Sum= 20(20+1)(40+1)/6

=20×21×41/6

=2870

for n = 4

sum= 4(4+1)(8+1)/6

=2×5×3

=30

∴5²+6²+7²+...20²

= 2870 - 30

= 2840

∴ Required sum is 2840

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