Solving inequalities. How to solve (x+5)/(3-x^2)≥ 0?

2 Answers
Apr 20, 2018

See details below

Explanation:

A fraction is positive or zero if and only if numerator and denominator have the same sign

Case 1.- Both positives
x+5>=0 then x>=-5 and
3-x^2>0 (imposible to be zero) then 3>x^2 that is

-sqrt3 < x < sqrt3

The intersection of both sets of values is [-5,oo)nn(-sqrt3,sqrt3)=(-sqrt3,sqrt3)

Case 2.- Both negatives

Similarly the solutions are (-oo,-5]nn((-oo,-sqrt3)uu(sqrt3,+oo))=

=[-5,-sqrt3)uu(sqrt3,+oo)

Now, the union of both cases will be the final result

[-5,-sqrt3)uu(-sqrt3,sqrt3)uu(sqrt3,+oo)

Apr 20, 2018

The solution is x in (-oo,-5]uu(-sqrt3, sqrt3)

Explanation:

The inequality is

(x+5)/(3-x^2)>=0

(x+5)/((sqrt3-x)(sqrt3+x))>=0

Let f(x)=(x+5)/((sqrt3-x)(sqrt3+x))

Let's build the sign chart

color(white)(aaaa)xcolor(white)(aaaa)-oocolor(white)(aaaa)-5color(white)(aaaa)-sqrt3color(white)(aaaa)+sqrt3color(white)(aaaa)+oo

color(white)(aaaa)x+5color(white)(aaaa)-color(white)(aaa)0color(white)(aaa)+color(white)(aaaaa)+color(white)(aaaaa)+

color(white)(aaaa)sqrt3+xcolor(white)(aaa)-color(white)(aaa)#color(white)(aaa)-#color(white)(aaa)||color(white)(aa)+color(white)(aaaaa)+

color(white)(aaaa)sqrt3-xcolor(white)(aaa)+color(white)(aaa)#color(white)(aaa)+#color(white)(aaa)#color(white)(aaa)+#color(white)(aa)||color(white)(aa)-

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

Therefore,

f(x)>=0 when x in (-oo,-5]uu(-sqrt3, sqrt3)

graph{(x+5)/(3-x^2) [-12.66, 12.66, -6.33, 6.33]}