Đặt A = 1.2 + 2.3 + 3.4 + ...... + 199.200
=> 3A = 1.2.(3 - 0) + 2.3.(4 - 1) + ..... + 199.200.(201 - 98)
=> 3A = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + .... + 199.200.201
=> 3A = 199.200.201
=> A = 199.200.201 : 3
=> A = 2 666 600
A=\(\frac{1.2+2.3+3.4+.....+20.21}{1+2-3-4+5+6-7-8+......+197+198-199-200+201}\)
Tính A
tinh tong A=1.2+2.3+3.4+4.5+...+2014.2015
TINH
A=1.2+2.3+ 3.4+...+99.100
Tinh A = 1.2+2.3+3.4+...+n.(n+1)
tinh tong A= 1.2^2+2.3^2+3.4^2+........+2018.2019^2
tinh
A=1/1.2+1/2.3+1/3.4+.........1/99.100
tinh gia tri cua bieu thuc A=1.2+2.3+3.4+...2005.2006
tinh
1.2+2.3+3.4+....+99.100
tinh tong S=1.2+2.3+3.4+...............+99.100
