Let f(x)=(x^2-4)/(3-x)=((x-2)(x+2))/(3-x)
The domain is D_f=RR-{3}
Let's do the sign chart
color(white)(aaaaa)xcolor(white)(aaaa)-oocolor(white)(aaaaa)-2color(white)(aaaaa)2color(white)(aaaaa)3color(white)(aaaaa)+oo
color(white)(aaaaa)x+2color(white)(aaaaa)-color(white)(aaaaaa)+color(white)(aaaa)+color(white)(aaa)+
color(white)(aaaaa)x-2color(white)(aaaaa)-color(white)(aaaaaa)-color(white)(aaaa)+color(white)(aaa)+
color(white)(aaaaa)3-xcolor(white)(aaaaa)+color(white)(aaaaaa)+color(white)(aaaa)+color(white)(aaa)-
color(white)(aaaaa)f(x)color(white)(aaaaaa)+color(white)(aaaaaa)-color(white)(aaaa)+color(white)(aaa)-
Therefore, f(x)>=0
when x in] -oo,-2 ] uu [2, 3[
graph{(x^2-4)/(3-x) [-34.51, 30.44, -18.83, 13.64]}