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August 7th, 2019, 11:14 PM   #1
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weird mistake?

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?

Last edited by skipjack; August 7th, 2019 at 11:37 PM.
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August 7th, 2019, 11:41 PM   #2
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Be careful when dividing by variables.

When they are negative the inequality flips direction.
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August 7th, 2019, 11:50 PM   #3
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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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August 14th, 2019, 12:37 AM   #4
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Quote:
Originally Posted by skipjack View Post
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
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