My Math Forum Algebra problem!

 Algebra Pre-Algebra and Basic Algebra Math Forum

 March 30th, 2009, 09:51 AM #1 Newbie   Joined: Mar 2009 Posts: 3 Thanks: 0 Algebra problem! I've got the following equation: 2?2x-5+4?2 belongs to Q i need to get x = -2 but don't know how to solve it!
 March 30th, 2009, 10:01 AM #2 Senior Member   Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3 Re: Algebra problem! What does "2?2x-5+4?2" mean? If this is a fraction, either use brackets, or put it between "code" tags and use preview to make sure it lines up.
 March 30th, 2009, 10:03 AM #3 Newbie   Joined: Mar 2009 Posts: 3 Thanks: 0 Re: Algebra problem!
 March 30th, 2009, 12:20 PM #4 Senior Member   Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3 Re: Algebra problem! "Belongs to Q" means "is rational" $2\sqrt2x-5+4\sqrt2= \sqrt2(2x+4) - 5$ Now, the "-5" is irrelevant, because a rational number minus five is still rational, and an irrational number minus five is still irrational. $\sqrt2(2x+4)$ This number can be rational if: (a) 2x+4 = 0, or (b) 2x+4 is some non-zero rational number times $\sqrt2$. This gives: (a) x = -2, or (b) an infinite number of answers, for example x=$\frac12(\sqrt2-4)$.
 March 31st, 2009, 06:18 AM #5 Newbie   Joined: Mar 2009 Posts: 3 Thanks: 0 Re: Algebra problem! THX for help!

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