a)[tex]2x^{2}+4x-6=0\\2(x^{2}+2x-3)=0\\x^{2}+2x-3=0\\x^{2}+3x-x-3=0\\x(x+3)-(x+3)=0\\(x+3)(x-1)=0\\x+3=0\\x-1=0\\x=-3\\x=1[/tex]
Vậy x=-3 hoặc x=1
b)[tex]x^{2}-x-12=0\\x^{2}+3x-4x-12=0\\x(x+3)-4(x+3)=0\\(x+3)(x-4)=0\\x+3=0\\x-4=0\\x=-3\\x=4[/tex]
Vậy x=-3 hoặc x=4