①.1/2*5+1/5*8+1/8*11+1/11*14=

问题描述:

①.1/2*5+1/5*8+1/8*11+1/11*14=
②.1/3*5+1/5*7+1/7*9+1/9*11=
③.3/4+3/28+3/70+3/130=
我会加悬赏分的!

第一题:1/2*5+1/5*8+1/8*11+1/11*14=1/3×[(1/2 - 1/5)+ (1/5 - 1/8)+ (1/8 - 1/11)+ (1/11 - 1/14)]=1/3 × (1/2 - 1/14)=1/3 ×3/7=1/7第二题1/3*5+1/5*7+1/7*9+1/9*11= 1/2×[(1/3 - 1/5)+ (1/5 - ...