How do you solve (x^2-4)/(3-x)>=0 using a sign chart?

1 Answer
Nov 19, 2016

The answer is x in] -oo,-2 ] uu [2, 3[

Explanation:

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]}