Question

1.2+2.3+3.4+...+99.100

Answer 1

tick tớ nha tớ tick lại cho

Answer 2

HOàng tick tớ nha

hehe

Answer 3

Đặt S = 1.2 + 2.3 + 3.4 +...+ 99.100

3S = 1.2.3 + 2.3.(4 - 1) + 3.4.(5 - 2) +...+ 99.100(101 - 98)

3S = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 +...+ 99.100.101 - 98.99.100

3S = 99.100.101

3S = 999900

S = 999900 : 3

S = 333300