(2/1-3/1)+(3/1-4/1)+(4/1+5/1)+......+(19/1-20/1)=?
(1-1/2)*(1-1/3)*(1-1/4)*(1-1/5)*(1-1/6)*…*(1-1/19)*(1-1/20)=
(1-1/2)×(1-1/3)×(1-1/4)×(1-1/5)×(1-1/6)×…×(1-1/19)×(1-1/20)=
(1-1/2+1/3-1/4+……+1/19-1/20)/[1/(11×20)+1/(12×19)+……+1/(15×1
1/(1×2)+1/(2×3)+1/(3×4)+1/(4×5).1/(19×20)等于多少?
(1+1/2)*(1+1/4)*(1+1/6)*...*(1+1/2008)*(1-1/3)*(1-1/5)*(1-1/
1/1×2+1/1-1/2:;1/2×4=1/2×(1/2-1/4);1/58×=1/3(×1/5-1/8)
1/(1*3)+1/(2*4)+1/(3*5)+1/(4*6)+...+1/(8*10)=?
1/6【1/4{1/3(1/2X-1)+3}+5】=1
(1+1/2)*(1+1/4)*.(1+1/10)*(1-1/3)*(1-1/5)*.(1-1/9)=?请写出过程和道理
(1+2/1)(1+4/1)(1+6/1).(1+10/)(1-3/1)(1—5/1).(1-9/1)
一道奥数题,急救!(1+1/2+1/3+1/4)×(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/
简算1/(2×3)+1/(3×4)+1/(4×5)+……+1/(18×19)+1/(19×20)