Powers and Roots Practice Test 1

Question : 24 of 40

Marks: +1, -0

The sum

11^2+12^2+...+21^2=?

Solution:

11^2+12^2+...+21^2

=(1^2+2^2+...+21^2)-(1^2+2^2 +...10^2)

={21(21+1)(2×21+1)}/6

-{10(10+1)(1 0×2+1)}/6

=19866/6-2310/6

=17556/6=2926

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