Question

   1^2+2^2+3^2+...2015^2

Answer 1

Đặt A = 1² + 2² + 3² + .... + 2015²

=> A = 1.1 + 2.2 + 3.3 + .... + 2015.2015

=> A = 1.( 2 - 1 ) + 2.( 3 - 1 ) + 3.( 4 - 1 ) + ... + 2015.( 2016 - 1 )

=> A = 1.2 - 1 + 2.3 - 2 + 3.4 - 3 + .... + 2015.2016 - 2015

=> A = ( 1.2 + 2.3 + 3.4 + .... + 2015.2016 ) - ( 1 + 2 + 3 + ... + 2015 )

=> A = \(\frac{2015.2016.2017}{3}-\frac{2015\left(2015+1\right)}{2}\)

=> A = 2731179360 - 2031120

=> A = 2729148240

Answer 2

ủng hộ tớ lên 40 nhé