1/3×1/4=1/3-1/4 1/5×1/6=1/5-1/6 1/6×1/7=1/6-1/7 找出他们的规律 根据规律再写三个算式找出规律 并计算 1/12+1/20+1/30 请写出规律 算式一步步请写详细

巧算：(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5+1/6)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5)(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5+1/6)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5)===== (1+1/2)*(1-1/2)*(1+1/3)*(1-1/3)*(1+1/4)*(1-1/4)*(1+1/5)*(1-1/5)=? 数学题(1/4+1/5+1/6+...+1/671)(1/3+1/4+1/5+..+1/670)-(1/3+1/4+1/5+...+1/671)(1/4+1/(1/4+1/5+1/6+...+1/671)(1/3+1/4+1/5+..+1/670)-(1/3+1/4+1/5+...+1/671)(1/4+1/5+1/6+...+1/670）=? 1 2 3 4 5=1 1()2()3()4()5=1 1+1-2+3-4+5=? 1/1*2+1/2*3+1/3*4+1/4*5+.+1/39*40=? 1/1*2+1/2*3+1/3*4+1/4*5+.+1/2004*2005=? 1/1*2+1/2*3+1/3*4+1/4*5+^+1/199*200=? 1/1*3+1/2*4+1/3*5+1/4*6+.+1/100*102=? 1-1/2+1/3-1/4+1/5-1/6+1/7.-1/50=? 1/3*4+1/4*5+.+1/29*30=? 1.（1+1/2+1/3+1/4）*（1/2+1/3+1/4+1/5）-（1+1/2+1/3+1/4+1/5）*（1/2+1/3+1/4）=2.（1+1/2+1/3+1/4+1/5）*（1/2+1/3+1/4+1/5+1/6）-（1+1/2+1/3+1/4+1/5+1/6）*（1/2+1/3+1/4+1/5）= (1+1/2+1/3+1/4+1/5)*(1/3+1/4+1)-(1+1/3+1/4)*(1/2+1/3+1/4+1/5) |3/1-2/1|+|4/1-3/1|+|5/1-4/1|+...+|10/1-9/1|=?3Q 1+2+3-4-5+1+1+2+3= 3+1/2+1/3+1/4+5=? (1+1/2+1/3+1/4)×(1/2+1+1/3+1/4+1/5)×(1/2+1/3+1/4) =简便方法