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=?
Tính S=1x2 + 2x3 + 3x4 +...+ 28x29 + 29x30
Tính nhanh:. A = 1x2 + 2x3 + 3x4 + 4x5 + ... + 99x100.
Tính nhanh:.
A = 1x2 + 2x3 + 3x4 + 4x5 + ... + 99x100.
1/2x3+1/3x4+1/4x5+,.......+1/29x30
Tính:
A=1x2+2x3+3x4+4x5+......+99x100+100x101
Tính tổng 1x2+2x3+3x4+4x5+.....+2014x2015
A=1x2+2x3+3x4+4x5+...+99x100
a.1x2+2x3+3x4+.........+19x20
b. 3x4+4x5+5x6+.........+49x50
