A = 1.2.3 + 2.3.4 + …. + 98.99.100
4A = 4( 1.2.3 + 2.3.4 + …. + 98.99.100)
4A= 1.2.3.4 + 2.3.4.4 +....+98.99.100.4
4A= 1.2.3.4 + 2.3.4 (5-1) +....+98.99.100(101- 97)
4A= 1.2.3.4 + 2.3.4.5 - 1.2.3.4 + ....+ 98.99.100.101 - 97.98.99.100
4A= 98.99.100.101
4A=97990200
A= 97990200:4
A=24497550
Vậy.....
tính hợp lí: A= 1/1.2.3+1/2.3.4+...+1/98.99.100
tính 1.2.3+2.3.4+3.4.5+....+98.99.100
Tính A = 1/1.2.3 + 1/2.3.4 + 1/3.4.5 + ............. + 1/ 98.99.100
Tính 1.2.3 + 2.3.4 + 3.4.5 + ... + 98.99.100
Tính 1.2.3 + 2.3.4 + .... + 98.99.100
Tính S = 1.2.3 + 2.3.4 + 3.4.5 + .... + 98.99.100
Tính tổng: 1/1.2.3+1/2.3.4|+...+1/98.99.100
tính
1.2.3+2.3.4.+3.4.5+........+98.99.100 bằng?
Tính : a, 1.2.3 + 2.3.4 + 3.4.5 + ... + (n - 1).n.(n+1)
b, 1.2.3 + 3.4.5 + 5.6.7 + 98.99.100
