Ax3= 1x2x3 + 2x3x3+.....+29x30x3
lấy B= 1x2x3+ 2x3x4+......+29x30x31
B- Ax3= 0 + 1x2x3+ 2x3x4+ 28x29x30= B- 29x30x31. Suy ra Ax3= 29x30x31
Cho A= 1x2+2x3+3x4+4x5+....+ 29x30 Tính Ax3=?
A=1x2+2x3+3x4+4x5+...+99x100
Tính nhanh:. A = 1x2 + 2x3 + 3x4 + 4x5 + ... + 99x100.
Tính nhanh:.
A = 1x2 + 2x3 + 3x4 + 4x5 + ... + 99x100.
a.1x2+2x3+3x4+.........+19x20
b. 3x4+4x5+5x6+.........+49x50
1x2 + 2x3 + 3x4 + 4x5 + .... +99x100
s=1x2+2x3+3x4+4x5+5x6
tinh nhanh A = 1x2 + 2x3 + 3x4 + 4x5 +.............+ 99x100
1x2+2x3+3x4+4x5+...2016x2017
