a) 3/8 - 1/6x = 1/4
1/6x= 3/8 - 1/4
1/6x=1/8
x= 1/8 : 1/6
x=3/4
Vậy x= 3/4
b)(x-1)^2 = 1/4
(x-1)^2= (+-2/4)^2
TH1 : (x-1)^2 = 2/4^2
.         x-1 = 2/4
.         x-1=1/2
.         x=1/2+1
.         x=3/2
TH2: (x-1)^2 = (-2/4)^2
.        x-1= -2/4
.        x= -2/4+1
.        x=1/2
Vậy x thuộc { 3/2;1/2}
c)(x- -1/2).(x+1/3)=0
TH1
x- (-1)/2=0
x          = 0 + (-1)/2
x          = -1/2
TH2
x+1/3=0
x       = 0-1/3
x       = -1/3 
Vậy x thuộc {-1/2;-1/3}

a) 1/3 +3/4-5/6
= 1/3 +3/4 + (-5)/6
= 4/12 + 9/12 + (-5)/6
= 13/12 + (-5)/6
= 13/12 + (-10)/12
= 3/12 = 1/4 
b) -2/3 + 6/5 : 2/3 - 2/15
= (-2)/3 + 6/5 . 3/2 - 2/15
= (-2/3) + 9/5 - 2/15
=15/15 = 1
c)(-3)/7+ 5/13+ (-4)/7
= [(-3)/7 + (-4)/7] + 5/13
= (-7)/7 + 5/13
=(-1) + 5/13
= -8/13
d)12/19 + (-8)/13 - 12/19 + 5/(-13) + 2
=12/19 + (-8)/13 - 12/19 +(-5)/13+ 2
= (12/19 - 12/19) + [ (-8)/13 + (-5)/13] + 2
= 0 + (-1) + 2
= -1