4) (x+2)(3x+4)=x2-4
<=> (x+2)(3x+4)=(x+2)(x-2)
<=> (x+2)(3x+4)-(x+2)(x-2)=0
<=> (x+2)(3x+4-x+2)=0
<=> (x+2)(2x+6)=0
<=> 2(x+2)(x+3)=0
<=> x=-2
x=-3
Vậy PT có S=\(\left\{-2;-3\right\}\)
11) 5(x-1)=3(x+1)-5
<=> 5x-5=3x+3-5
<=> 5x-3x=3-5+5
<=> 2x=3
<=> x=\(\frac{3}{2}\)
Vậy......