20/1+19/1+18/1……1@+1/1=
20/1+19/1+18/1……1@+1/1=
计算:20-19+18-……-3+2-1=?
1+2+3+4+5+…+18+19+20=
1/1*2*3+1/2*3*4+……+1/18*19*20
1/2*3*4+1/2*3*4+3*4*5+……1/18*19*20=
巧算:1/1*2+1/2*3+1/3*4+……1/19*20+1/20*21=
(1-1/2)*(1-1/3)*(1-1/4)*(1-1/5)*(1-1/6)*…*(1-1/19)*(1-1/20)=
1-1/2+1/3-1/4+1/5-1/6+1/7-1/8+1/9……+1/19-1/20=?
(1-1/2+1/3-1/4+……+1/19-1/20)/[1/(11×20)+1/(12×19)+……+1/(15×1
20-19+18-17+……+4-3+2-1=?
算式(3/1-4/1)+(4/1-5/1)……+(20/1-19/1)求解
计算(1/2+1/3)+(2/3+1/4)+(3/4+1/5)……+(18/19+1/20)+(19/20+1/2)!