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 August 7th, 2019, 11:14 PM #1 Newbie   Joined: Jul 2019 From: jakarta Posts: 3 Thanks: 2 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.
 August 7th, 2019, 11:41 PM #2 Senior Member     Joined: Sep 2015 From: USA Posts: 2,529 Thanks: 1389 Be careful when dividing by variables. When they are negative the inequality flips direction. Thanks from topsquark and nanaseailie
 August 7th, 2019, 11:50 PM #3 Global Moderator   Joined: Dec 2006 Posts: 20,921 Thanks: 2203 The first step "reverses" the inequality if x < 0. Multiplying by x² instead leads to the correct solution: x < -3 or x > 0. Thanks from greg1313, topsquark and nanaseailie
August 14th, 2019, 12:37 AM   #4
Newbie

Joined: Jul 2019
From: jakarta

Posts: 3
Thanks: 2

Quote:
 Originally Posted by skipjack 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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