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

1 Answer
Nov 28, 2017

The solution is x in (-oo, -2) uu [0, 4]

Explanation:

Let

f(x)=(x(4-x))/(x+2)

Let's build the sign chart

color(white)(aaaa)xcolor(white)(aaaa)-oocolor(white)(aaaaa)-2color(white)(aaaaaa)0color(white)(aaaaaa)4color(white)(aaaaa)+oo

color(white)(aaaa)x+2color(white)(aaaaaa)-color(white)(aa)||color(white)(aaa)+color(white)(aaaa)+color(white)(aaaaa)+

color(white)(aaaa)xcolor(white)(aaaaaaaaaa)-color(white)(aa)||color(white)(aa)-color(white)(aa)0color(white)(aa)+color(white)(aaaaa)+

color(white)(aaaa)4-xcolor(white)(aaaaaaa)+color(white)(aa)||color(white)(aa)+color(white)(aa)#color(white)(aaa)+#color(white)(aa)0color(white)(aa)-

color(white)(aaaa)f(x)color(white)(aaaaaaaa)+color(white)(aa)||color(white)(aa)-color(white)(aa)0color(white)(aa)+color(white)(aa)0color(white)(aa)-

Therefore,

f(x)>=0 when x in (-oo, -2) uu [0, 4]

graph{(x(4-x))/(x+2) [-38.63, 43.6, -7.9, 33.2]}