简便计算:1/20+1/30+1/42+.+1/132=?
问题描述:
简便计算:1/20+1/30+1/42+.+1/132=?
答
1/20+1/30+1/42+......+1/132
=(5 -4)/(4 *5) +(6 -5)/(5 *6)+(7 -6)/(6 *7)+......(12 -11)/(11 *12)
=1/4-1/5+1/5-1/6+----+1/11-1/12
=1/4-1/12
=1/6
答
1/20+1/30+1/42+.+1/132
=1/4-1/5+1/5-1/6+...+1/11-1/12
=1/4-1/12
=1/6