2/1×3+2/3×5+2/5×7+2/19×21
2/1*3+2/3*5+2/5*7+.+2/17*19+2/19*21=?
2/3×1+2/3×5+2/5×7…2/19×21
2/1×3+2/3×5+2/5×7+2/19×21
2/1×3+2/3×5+2/5×7+···+2/19×21
1/2+1/3+3/4+2/5+5/7+7/8+9/20+10/21+11/24+19/35
1又3/14-19/21 1.4-4/9-2/5+2/3 1/2+2/5-3/10+0.6 1/2+3/4+7/8+15
数学简算题两道 (1)1/1*3+1/3*5+1/5*7+.+1/17*19+1/19*21 (2)1/1*2+1/2*
1-2+3-4+5-6~~+19-20+21
1/3-1/5=2/3*5,计算1/3*5+1/5*7+1/7*9+…+1/19*21
1/3+3/4+2/5+5/7+7/8+9/20+10/21+11/24+19/35=?
简算:1/3+3/4+2/5+5/7+7/8+9/20+10/21+11/24+19/35
1/3+3/4+2/5+7/5+7/8+9/20+10/21+11/24+19/35