a)[tex]9x^2-6x-3=0[/tex]
<=>[tex]9x^2-6x+1-4=0[/tex]
<=>[tex](3x-1)^2-4=0[/tex]
<=> [tex](3x-1-2)(3x-1+2)=0[/tex]
=>3x-3=0 hoặc 3x+1=0
=>x= 1 hoặc x= [tex]-\frac{1}{3}[/tex]
b)[tex](2x+1)^2-4(x+2)^2=9[/tex]
<=>[tex][2x+1+2(x+2)].[2x+1-2(x+2)]=9[/tex]
<=>[tex](4x+5).(-3)=9[/tex]
<=>4x+5=-3
=>x= -2
c)[tex]3(x-1)^2-3x(x-5)=21[/tex]
<=>[tex]3(x^2-2x+1)-3x^2+15=21[/tex]
<=>[tex]3x^2-6x+3-3x^2+15x=21[/tex]
<=>9x=18
=>x=2
d)[tex](x+3)^2-(x-4)(x+8)=1[/tex]
<=>[tex]x^2+6x+9-(x^2+8x-4x-32)=1[/tex]
<=>[tex]x^2+6x+9-x^2-4x+32=1[/tex]
<=>2x+41=1
<=>2x=-40
=>x=-20