4xA=1x2x3x4+2x3x4x4+3x4x5x4+...+15x16x17x4
4xA=1x2x3x4+2x3x4x(5-1)+3x4x5x(6-2)+...+-15x16x17x(18-14)
4xA=1x2x3x4-1x2x3x4+2x3x4x5-2x3x4x5+3x4x5x6-...-14x15x16x17+15x16x17x18=15x16x17x18
=> A=15x4x17x18=18360
Các câu hỏi tương tự
1x2x3 + 2x4x6 + 3x6x9/2x3x4 + 4x6x8 + 6x9x12
tính a =1x2x3+2x3x4+.........+100x101x102
1x2x3+2x4x6+3x6x9+4x8x12/2x3x4+4x6x8+6x9x12+8x12x16
giải hộ với:
C= 1x2x3+2x3x4+...........+8x9x10
1/1x2x3+1/2x3x4+1/3x4x5+...+1/89x99x100
Cho A = 1x2x3 + 2x3x4 + 3x4x5 + ....... +49x50x51
Tinh A
Tính: A=1x2x3 + 2x3x4 +…+ 100x101x102
A=1/1x2x3+1/2x3x4+1/3x4x5+...+1/18x19x20<1/4
tim A biet A = 1x2x3+2x4x6+4x8x12+8x16x24/2x3x4+4x6x8+8x12x16+16x24x32