Question

Tính tổng E=1.2.3+3.4.5+5.6.7+...+99.100.101

Answer 1

=> 4E = 1.2.3.4 + 2.3.4.4 + 3.4.5.4 + .... + 99.100.101.4

=> 4E = 1.2.3.( 4 - 0 ) + 2.3.4.( 5 - 1 ) + 3.4.5.( 6 - 2 ) + .... + 99.100.101.( 102 - 98 )

=> 4E = 1.2.3.4 - 0.1.2.3 + 2.3.4.5 - 1.2.3.4 + 3.4.5.6 - 2.3.4.5 + ... + 99.100.101.102 - 98.99.100.101

=> 4E = ( 1.2.3.4 - 1.2.3.4 ) + ( 2.3.4.5 - 2.3.4.5 ) +  + ... + ( 98.99.100.101 - 98.99.100.101 ) + 99.100.101.102

=> 4E = 99.100.101.102

=> E = ( 99.100.101.102 ) : 4