How do you solve p/(p-16)+2/(p-6)<=0 using a sign chart?

1 Answer
May 7, 2017

The solution is p in [-4,6) uu [8, 16)

Explanation:

Let 's simplify the LHS of the inequality

p/(p-16)+2/(p-6)<=0

(p(p-6)+2(p-16))/((p-16)(p-6))<=0

(p^2-6p+2p-32)/((p-16)(p-6))<=0

(p^2-4p-32)/((p-16)(p-6))<=0

((p+4)(p-8))/((p-16)(p-6))<=0

Let f(p)=((p+4)(p-8))/((p-16)(p-6))

We can build the sign chart

color(white)(aaaa)pcolor(white)(aaaa)-oocolor(white)(aaaa)-4color(white)(aaaaaaa)6color(white)(aaaaaa)8color(white)(aaaaaaa)16color(white)(aaaa)+oo

color(white)(aaaa)p+4color(white)(aaaa)-color(white)(aaaaaa)+color(white)(aaa)||color(white)(aaa)+color(white)(aaa)+color(white)(aaa)||color(white)(aa)+

color(white)(aaaa)p-6color(white)(aaaa)-color(white)(aaaaaa)-color(white)(aaa)||color(white)(aaa)+color(white)(aaa)+color(white)(aaa)||color(white)(aa)+

color(white)(aaaa)p-8color(white)(aaaa)-color(white)(aaaaaa)-color(white)(aaa)||color(white)(aaa)-color(white)(aaa)+color(white)(aaa)||color(white)(aa)+

color(white)(aaaa)p-16color(white)(aaa)-color(white)(aaaaaa)-color(white)(aaa)||color(white)(aaa)-color(white)(aaa)-color(white)(aaa)||color(white)(aa)+

color(white)(aaaa)f(p)color(white)(aaaaa)+color(white)(aaaaaa)-color(white)(aaa)||color(white)(aaa)+color(white)(aaa)-color(white)(aaa)||color(white)(aa)+

Therefore,

f(p)<=0 when p in [-4,6) uu [8, 16)