Question

(1x1+2x2+3x3+.....+9x9)x1=

Answer 1

Exista formula generala pentru suma patratelor de numere consecutive:

$1^{2} + 2^{2} + 3^{2} +...+ n^{2} = \frac{n(n+1)(2n+1)}{6}$

deci suma cautata este:

$1^{2} + 2^{2} + 3^{2} +...+ 9^{2} = \frac{9(9+1)(2*9+1)}{6}$=285