How do you solve x/(x-2)> -1/(x+3) using a sign chart?

1 Answer
Dec 10, 2017

The solution is x in (-oo,-4.45] uu(-3, 0.45] uu (2, +oo)

Explanation:

Simplify the inequality, we cannot do crossing over.

x/(x-2) > -1/(x+3)

x/(x-2)+1/(x+3)>0

(x(x+3)+(x-2))/((x-2)(x+3))>0

(x^2+3x+x-2)/((x-2)(x+3)) >0

(x^2+4x-2)/((x-2)(x+3)) >0

The roots of the numerator

x^2+4x-2=0

are

x=(-4+-sqrt(16-4(1)(-2)))/(2)

=-2+-sqrt6

x_1=-2-sqrt6=-4.45

x_2=-2+sqrt6=0.45

Let

f(x)=((x-x_1)(x-x_2))/((x-2)(x+3))

We can build the sign chart

color(white)(aaaa)xcolor(white)(aaaa)-oocolor(white)(aaaa)x_1color(white)(aaaa)-3color(white)(aaaaa)x_2color(white)(aaaaa)2color(white)(aaaaa)+oo

color(white)(aaaa)x-x_1color(white)(aaaa)-color(white)(aaaa)+color(white)(aaaa)+color(white)(aaaa)+color(white)(aaaa)+color(white)(aaaa)

color(white)(aaaa)x-3color(white)(aaaaa)-color(white)(aaaa)-color(white)(aa)||color(white)(a)+color(white)(aaaa)+color(white)(aaaa)+

color(white)(aaaa)x-x_2color(white)(aaaa)-color(white)(aaaa)-color(white)(aa)#color(white)(aa)-#color(white)(aaaa)+color(white)(aaaa)+

color(white)(aaaa)x-2color(white)(aaaaa)-color(white)(aaaa)-color(white)(aa)#color(white)(aa)-#color(white)(aaaa)-color(white)(aa)||color(white)(a)+

color(white)(aaaa)f(x)color(white)(aaaaaa)+color(white)(aaaa)-color(white)(aa)||color(white)(a)+color(white)(aaaa)-color(white)(aa)||color(white)(a)+

Therefore,

f(x) >0 when x in (-oo,-4.45] uu(-3, 0.45] uu (2, +oo)

graph{(x^2+4x-2)/((x-2)(x+3)) [-10, 10, -5, 5]}