(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)怎么做,求讲解 (1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)求讲解!

(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)怎么做,求讲解 (1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)求讲解!
(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)怎么做,求讲解
(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)求讲解!

(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)怎么做,求讲解 (1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)求讲解!
令a=1/2+1/3+1/4
则1+1/2+1/3+1/4=1+a
1/2+1/3+1/4+1/5=a+1/5
1+1/2+1/3+1/4+1/5=1+a+1/5
所以原式=(1+a)(a+1/5)-a(1+a+1/5)
=a(1+a)+(1+a)*1/5-a(1+a)-a*1/5
=(1+a)*1/5-a*1/5
=1/5+a*1/5-a*1/5
=1/5

(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)
=(1/2+1/3+1/4+1/5)+【(1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)】
-【(1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)】-(1/2+1/3+1/4)
=(1/2+1/3+1/4+1/5)-(1/2+1/3+1/4)
=1/5