Question

11^2+ 12^2+13^2+.........+20^2=?​

Answer 1

Step-by-step explanation:

11^2 + 12^2 + 13^2 + ... + 20^2) = (1^2 + 2^2 + 3^2 + ... + 20^2) - (1^2 + 2^2 + 3^2 + ... + 10^2)

Ref: (1^2 + 2^2 + 3^2 + ... + n^2) = 1 /6n(n + 1)(2n + 1)

= 20 x 21 x 41 - 10 x 11 x 21

= (2870 - 385)

= 2485.