高校问答笔迹书写时间同一鉴定:简单的计算（简便方法）
来源：百度文库 编辑：高校问答 时间：2024/04/30 18:39:55
2)1/6+1/12+1/20+1/30+1/42
1)38*103/138+35*37/138
==(38*103+35*37)/138
==[(37+1)*103+35*37]/138
==[37*103+103+35*37]/138
==[37*(103+35)+103]/138
==[37*138+103]/138
==37+103/138
运算方法：
凑数使得分子与分母进行约分。
2)1/6+1/12+1/20+1/30+1/42
==1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)
==1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
==1/2+(-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6)-1/7
==1/2-1/7
==5/14
运算方法：
1/(mn)==(1/m-1/n)/(n-m)
1)38*103/138+35*37/138
==(38*103+35*37)/138
==[(37+1)*103+35*37]/138
==[37*103+103+35*37]/138
==[37*(103+35)+103]/138
==[37*138+103]/138
==37+103/138
运算方法：
凑数使得分子与分母进行约分。
2)1/6+1/12+1/20+1/30+1/42
==1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)
==1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
==1/2+(-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6)-1/7
==1/2-1/7
==5/14
运算方法：
1/[(n-1)n]==1/(n-1)-1/n
2:
=1/2-1/3+1/3-1/4+1/4-1/5+...+1/6-1/7=1/2-1/7
=5/14
1)38*103/138+35*37/138
==(38*103+35*37)/138
==[(37+1)*103+35*37]/138
==[37*103+103+35*37]/138
==[37*(103+35)+103]/138
==[37*138+103]/138
==37+103/138
==140/138
==70/69
2)1/6+1/12+1/20+1/30+1/42
==1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)
==1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
==1/2+(-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6)-1/7
==1/2-1/7
==5/14
=5/14