How do you solve (2x)/(x-5)>=3?

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1 Answer
Aug 4, 2018

The solution is x in (5,15]

Explanation:

You cannot do crossing over in inequalities

(2x)/(x-5)>=3

<=>, (2x)/(x-5)-3>=0

<=>, (2x-3(x-5))/(x-5)>=0

<=>, (2x-3x+15)/(x-5)>=0

<=>, (-x+15)/(x-5)>=0

Let f(x)=(-x+15)/(x-5)

Build a sign chart

color(white)(aaaa)xcolor(white)(aaaa)-oocolor(white)(aaaaaaa)5color(white)(aaaaaaa)15color(white)(aaaa)+oo

color(white)(aaaa)x-5color(white)(aaaaa)-color(white)(aaaa)||color(white)(aa)+color(white)(aaaaaa)+

color(white)(aaaa)-x+15color(white)(aaa)+color(white)(aaaaa)#color(white)(aa)+#color(white)(aaa)0color(white)(aa)-

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

Therefore,

f(x)>=0 when x in (5,15]

graph{(2x)/(x-5)-3 [-25.56, 32.17, -14.65, 14.22]}