Giải thích các bước giải:
Bài 1 :
3S=`(5-2)/(2.5)`+`(8-5)/(5.8)`+`(11-8)/(8.11)`+....................+`(43-40)/(40.43)`
3S=`1/2`-`1/5`+`1/5`-`1/8`+............................+`1/40`-`1/43`
3S=`1/2`-`1/43`=`41/86`
=>x=`41/86` : 3
Bài 2 :
a)
/x-`1/6`/=75%
=>x-`1/6` = `3/4` hoặc x-`1/6`=`-3/4`
=>x=`11/12` hoặc x = `-7/12`
b)`2/5`+`3/5`x=`9/10`
=>`3/5`x=`9/10`-`2/5`=`1/2`
=>x=`1/2`:`3/5`=`5/6`
c)`1/3`+`2/3` : x = -1`1/5`
=>`1/3`+`2/3`:x = `-6/5`
=>`2/3` : x = `-6/5`-`1/3`=`-23/15`
=>x = `2/3` : `-23/15` = `30/69`=`10/23`