Question

Tính tổng S=1.2+2.3+3.4+.....+99.100

Answer 1

3S=1.2.3+2.3.3+...+99.100.3

3S=1.2(3-0)+2.3(4-1)+...+99.100(101-98)

3S=(1.2.3-0.1.2)+(2.3.4-1.2.3)+...+(99.100.101-98.99.100)

3S=99.100.101

3S=999900

S=333300