How do you solve 2/(p-1)>=3/4 using a sign chart?

4 Answers
Jan 6, 2018

p in (1,11/3]

Explanation:

2/(p-1)>=3/4

2/(p-1)-3/4>=0

(2*4-3(p-1))/(4(p-1))>=0

(11-3p)/(4(p-1))>=0

zero points:
p_1=11/3

p_2=1

[[,|,-oo;1,1;11/3,11/3;oo],[11-3p,|,+,+,-],[p-1,|, -,+,+]]

p in (-oo,1)hArr function is negative

color(red)(p in (1,11/3)hArr "function is positive")

p in (11/3,oo)hArr function is negative

But the function may equal to zero which is only when p=11/3. Therefore we include 11/3 to the asnwer.

Jan 6, 2018

The solution is p in (1,11/3]

Explanation:

Simplify the inequality

2/(p-1)>=3/4

2/(p-1)-3/4>=0

Putting on the same denominator

((2*4-3*(p-1)))/(4(p-1))>=0

(8-3p+3)/(4(p-1))>=0

(11-3p)/(4(p-1))>=0

Let f(p)=(11-3p)/(4(p-1))

Construct the sign chart

color(white)(aaaa)pcolor(white)(aaaa)-oocolor(white)(aaaaaa)1color(white)(aaaaaaa)11/3color(white)(aaaa)+oo

color(white)(aaaa)p-1color(white)(aaaaa)-color(white)(aaaa)||color(white)(aaaa)+color(white)(aaaaa)+

color(white)(aaaa)11-3pcolor(white)(aaa)+color(white)(aaaa)#color(white)(aaaaa)+#color(white)(aa)0color(white)(aa)-

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

Therefore,

f(p) >=0 when p in (1,11/3]

graph{(11-3x)/(4(x-1)) [-12.66, 12.65, -6.33, 6.33]}

Jan 6, 2018

I never really did them this way. But, here is an excellent tutorial and example: http://www.fmaths.com/signcharts/lesson.php

Explanation:

Check the link to see the steps required for this particular problem.

Jan 6, 2018

Ulternate approach

Explanation: