1/2+1/6+1/12+1/20+1/30+1/42怎么简便计算将长方形一刀分为两个部分,拼成直角三角形一直∠a=34°25’,则∠a的余角为

Question

1/2+1/6+1/12+1/20+1/30+1/42 怎么简便计算
将长方形一刀分为两个部分,拼成直角三角形
一直∠a=34°25’,则∠a的余角为

Answer 1

1/2+1/6+1/12+1/20+1/30+1/42
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7
∠a的余角为90°-34°25’=55°35’