1/4*5+1/5*6+1/6*7+……+1/39*40
1/4*5+1/5*6+1/6*7+……+1/39*40
1/4×5+1/5×6+1/6×7+……+1/39×40
1+2+3+4+5+6+7+8+9+10+……+40=?
1/3*4+1/4*5+1/5*6+1/6*7+……+1/99*100=?求规律!
2+4+6+……+200= 17+19+21+……+39= (2+4+6+……+2000)-(1+3+5+……+1999
1/2×4+1/3×5+1/4×6+1/5×7+……+1/8×10+1/9×11
1/2+1/3+1/4+1/5+1/6+1/7+……+1/2000+1/2001
1/1×3+1/3×5+1/5×7+…………+1/49×51和1/2×4+1/4×6+1/6×8+…………1/48×50
4×5分之1+5×6分之1+6×7分之1+.39×40分之1 简便
1/4×5+1/5×6+1/6×7+.1/39×40简便算法
简算:1/4×5+1/5×6+1/6×7..+1/39+40
-1/2,2/3,-3/4,4/5,-5/6,6/7……