weird mistake?

Jul 2019
6
2
jakarta
Guys, I need help in reasoning this:
(7x+12)/x > 3
7x+12 > 3x
4x > -12
x > -3

but if you sketch the graph it's obvious that my answer is wrong.
What is wrong with the steps?:cold:
 
Last edited by a moderator:

romsek

Math Team
Sep 2015
2,960
1,674
USA
Be careful when dividing by variables.

When they are negative the inequality flips direction.
 
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skipjack

Forum Staff
Dec 2006
21,478
2,470
The first step "reverses" the inequality if x < 0.

Multiplying by x² instead leads to the correct solution: x < -3 or x > 0.
 
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Jul 2019
6
2
jakarta
The first step "reverses" the inequality if x < 0.

Multiplying by x² instead leads to the correct solution: x < -3 or x > 0.
I see, didnt think of it that multiplying by x squared will do the job.
thank you sir