4:
a: =>1/5-x=2/5:1/3=6/5
=>x=-1
b: =>3/5*x=7/12
=>x=7/12:3/5=7/12*5/3=35/36
c: =>3/4:x=-9/4
=>x=-3/4:9/4=-1/3
d: =>2(2x-3)=5/4
=>2x-3=5/8
=>2x=29/8
=>x=29/16
f: =>2x+1/2=0 hoặc 2x-3=0
=>x=-1/4; x=3/2
h: =>(2x+1/2)^2=1/4
=>2x+1/2=1/2 hoặc 2x+1/2=-1/2
=>x=-1/2 hoặc x=0
i: =>(3x-1/2)^2=16/25
=>3x-1/2=4/5 hoặc 3x-1/2=-4/5
=>x=13/30 hoặc x=-1/10
