Tính nhanh
\TÍNH NHANH:
2/1x2 + 2/2x3 + 2/3x4 + 2/4x5 + 2/5x6 +2/6x7 + 2/7x8 + 2/8x9 + 2/9x10 +2/10x11 + 2/11x12 + 2/12x13 +2/13x14 + 2/14x15 + 2/15x16 + 2/16x17 + 2/17x18 + 2/18x19 + 2/19x20 =
LƯU Ý:
2/1x2 - 2 + ....
1x2
2/1x2 + 2/2x3 + 2/3x4 + 2/4x5 + 2/5x6 +2/6x7 + 2/7x8 + 2/8x9 + 2/9x10 +2/10x11 + 2/11x12 + 2/12x13 +2/13x14 + 2/14x15 + 2/15x16 + 2/16x17 + 2/17x18 + 2/18x19 + 2/19x20 =
LƯU Ý:
2/1x2 - 2 + ....
1x2