1/6:1/7:1/8=56:48:42是怎么算

1/6:1/7:1/8=56:48:42是怎么算 1+2又1/8+3又1/12+5又1/30+6又1/42+7又1/56+8又1/42+9又1/42=? 1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9=1-1/9=8/9为什么呢?写出解析. 请问：速算（巧算）...请阅题：第一题：1/16+1/32+1/64+1/128=?第二题：1/2+1/6+1/12+1/20+1/30+1/42+1/56=?第三题：1+2又1/6+3又1/12+4又1/20+6又1/42+7又1/56+8又1/72+9又1/90 这四道题用简便方法1/1*2+1/2*3+1/3*4+1/4*5= 1/1*6+1/6*11+1/11*16+1/16*21= 1/6+1/12+1/20+1/30+1/42+1/56= 1/8+1/24+1/48+1/120= 请教数学题（6+1/42+7+1/56+8+1/72.+20+1/420=?请把答案道理写清楚, 学而思2010年奥数寒假作业1+1/3+1/6+1/10+1/15+1/21+1/28=( )(2*2)/(1*3)+(4*4)/(3*5)+(6*6)/(5*7)+(8*8)/(7*9)+(10*10)/(9*11)=( )1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=( )*=乘号/=分数线 1/2+1/6+1/12+1/20+1/30+1/42+1/56怎么做?我已经知道算式了,但我想求答案.1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8=（一个算式）=得数. 1+2又1/6+3又1/12+4又1/20+5又1/30+6又1/42+7又1/56+8又1/72+9又1/90= 1+2又6/1+3又12/1+4又20/1+5又30/1+6又42/1+7又56/1+8又72/1+9又90/1=? 1/2+1/6+1/12+1/20+1/30+1/42+1/56=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8=1-1/8=7/8这一步=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8怎么会得到这步=1-1/8 1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=______1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90 ＝1/（1*2）+1/（2*3）+1/（3*4）+1/（4*5）+1/（5*6）+1/（6*7）+1/（7*8）+1/（8*9）+1/（9*10） ＝1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1 2/1+2又6/1+3右12/1+4又20/1+5又30/1+6又42/1+7又56/1+8又72/1=?/是表示分之 1+2又1/8+3又1/12+4又1/20+5又1/30-6又1/42+7又1/56+8又1/42+9又1/42 1又1/20+2又1/30+3又1/42+4又1/56+5又1/72+6又1/90+7又1/110+8又1/132=? 2/1+6/1+12/1+20/1+30/1+42/1+56/1=? 2/1+6/1+12/1+20/1+30/1+42/1+56/1= 1/2+1/6+1/12+1/20+1/30+1/42+1/56=