2/2*4+2/4*6+2/6*8+2/8*10+2/10*12的计算
问题描述：
2/2*4+2/4*6+2/6*8+2/8*10+2/10*12的计算
答
2/2*4+2/4*6+2/6*8+2/8*10+2/10*12
=1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12
=1/2-1/12
=5/12
答
2/(n*(n+2))=1/n-1/(n+2)
2/2*4+2/4*6+2/6*8+2/8*10+2/10*12
=1/2-1/4+1/4-1/6+...+1/10-1/12
=1/2-1/12
=5/12