Bài 1: a,31/17 + -5/13+ -8/13- 14/17 =(31/17- 14/17)+(-5/13+ -8/13) =1+(-1) =0
b,5/7 . 2/11 + -5/7 . 9/11 + 5/7 =5/7.(2/11+9/11+1) =5/7.2 =10/7
Bài 2: a,x - 1/4 = 2/15 x = 2/15+1/4 x =8/60+15/60 x =23/60
b,x + 7/12 = 17/18 - 1/9 x + 7/12 = 17/18 - 2/18 x + 7/12 = 5/6 x = 5/6-7/12 x = 10/12-7/12 x = 1/4
c, x/45 = 5/6 + -29/30 x/45 = 25/30+ -29/30 x/45 =-2/15 => x.15=45.-2 x.15=-90 x =-90:15 x =-6