1/1*3+1/2*4+1/3*5+1/4*6+.+1/18*20
1/1*3+1/2*4+1/3*5+1/4*6+.+1/18*20
1/1*2*3+1/2*3*4+1/3*4*5+.+1/18*19*20
1/1*3+1/2*4+1/3*5+1/4*6+1/5*7+1/6*8------1/17*19+1/18*20 如何用
1/1*3+1/2*4+1/3*5+1/4*6+1/5*7+1/6*8------1/17*19+1/18*20 怎样做
1/1*3+1/2*4+1/3*5+1/4*6+1/5*7+1/6*8------1/17*19+1/18*20
求1/2*3+1/3*4+1/4*5+.+1/18*19+1/19*20
1/2×3+1/3×4+1/4×5+.+1/18×19+1/19×20等于?
简算1/2*3+1/3*4+1/4*5+.+1/18*19+1/19*20
1/2*3+1/3*4+1/4*5+.+1/18*19+1/19*20=?
1*3/1+2*4/1+3*5/1+4*6/1.+18*20/1怎么算?
1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1 1 6 15 20 15 6 1
(1\2+1\3)+(2\3+1\4)+(3\4+1\5)+(4\5+1\6)+.+(18\19+1\20)+(19\2