(1/4 ×6/1+6/1×8/1+8/1×10/1+10/1×12/1)×2这道题怎么简便算?
问题描述：
(1/4 ×6/1+6/1×8/1+8/1×10/1+10/1×12/1)×2这道题怎么简便算?
答
(1/4*1/6+1/6*1/8+1/8*1/10+1/10*1/12)*2
=[(1/4-1/6)*1/2+(1/6-1/8)*1/2+(1/8-1/10)*1/2+(1/10-1/12)*1/2]*2
=[(1/4-1/6)+(1/6-1/8)+(1/8-1/10)+(1/10-1/12)]*2*1/2
=(1/4-1/6)+(1/6-1/8)+(1/8-1/10)+(1/10-1/12)
=1/4-1/12
=3/12-1/12
=2/12
=1/6