[tex]y=x^2+3x-4\\x+y-8=0\\\\y=x^2+3x-4\\y=-x+8\\\\x^2+3x-4=-x+8\\x^2+4x-12=0\\x^2+6x-2x-12=0\\x(x+6)-2(x+6)=0\\(x-2)(x+6)=0\\x=2 \vee x=-6\\\\y=-2+8 \vee y=-(-6)+8\\y=6 \vee y=14\\\\(x,y)\in\{(2,6),(-6,14)\}[/tex]
