早教吧作业答案频道 -->数学-->
问一组数学题2/42+2/56+2/72+2/90+2/110+2/132
题目详情
问一组数学题2/42+2/56+2/72+2/90+2/110+2/132
▼优质解答
答案和解析
=2*(1/42+1/56+1/72+1/90+1/110+1/132)
=2*(1/(6*7)+...+1/(11*12))
=2*(1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11+1/11-1/12)
=2*(1/6-1/12)
=2*1/12
=1/6
裂项原理 1/n-1/(n+1)=1/((n+1)n)
=2*(1/(6*7)+...+1/(11*12))
=2*(1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11+1/11-1/12)
=2*(1/6-1/12)
=2*1/12
=1/6
裂项原理 1/n-1/(n+1)=1/((n+1)n)
看了 问一组数学题2/42+2/5...的网友还看了以下：