How do you solve (x^2+5x)/(x-3)>=0 using a sign chart?

1 Answer
Jan 21, 2017

The answer is x in [-5,0 ] uu ] 3, +oo [

Explanation:

Let f(x)=(x^2+5x)/(x-3)=(x(x+5))/(x-3)

The domain of f(x) is D_f(x)=RR-{3}

Let's do the sign chart

color(white)(aaaa)xcolor(white)(aaaa)-oocolor(white)(aaaa)-5color(white)(aaaaa)0color(white)(aaaaaaaaa)3color(white)(aaaaa)+oo

color(white)(aaaa)x+5color(white)(aaaaa)-color(white)(aaaa)+color(white)(aaaaa)+color(white)(aaaa)color(red)(∥)color(white)(aa)+

color(white)(aaaa)xcolor(white)(aaaaaaaa)-color(white)(aaaa)-color(white)(aaaaa)+color(white)(aaaa)color(red)(∥)color(white)(aa)+

color(white)(aaaa)x-3color(white)(aaaaa)-color(white)(aaaa)-color(white)(aaaaa)-color(white)(aaaa)color(red)(∥)color(white)(aa)+

color(white)(aaaa)f(x)color(white)(aaaaaa)-color(white)(aaaa)+color(white)(aaaaa)-color(white)(aaaa)color(red)(∥)color(white)(aa)+

Therefore,

f(x)>=0, when x in [-5,0 ] uu ] 3, +oo [