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 February 4th, 2010, 04:10 PM #1 Newbie   Joined: Feb 2010 Posts: 3 Thanks: 0 Linear Systems of Equations: Substition Method Why is that everytime I solve x in terms of y and substitute, I get a different answer (wrong)? I am trying to understand the intuition behind it.... ex: y=15-5x y=25-5x parallel lines means no unique solution substitute y in terms of x SUBSTITUTION 1: y=15-5x (15-5x)=25-5x 0=0 substitute x in terms of y SUBSTITUTION 2: y=15-5x therefore,5x=15-y y=25-(15-y) 2y=10 y=5 Makes no sense??? February 4th, 2010, 06:42 PM #2 Newbie   Joined: Feb 2010 Posts: 3 Thanks: 0 Re: Linear Systems of Equations: Substition Method lol anyone??? February 5th, 2010, 01:39 PM #3 Global Moderator   Joined: May 2007 Posts: 6,807 Thanks: 716 Re: Linear Systems of Equations: Substition Method The particular pair of equations you chose has no solution. You can easily see that by subtracting one from the other and get as an equation 15=25. February 7th, 2010, 04:57 AM #4 Newbie   Joined: Feb 2010 Posts: 3 Thanks: 0 Re: Linear Systems of Equations: Substition Method yes i am aware of this.... and you can prove it using substition... but my question is why is it that you can only solve systems of linear equations by substituing y in terms of x, and not x in terms of y? substitute y in terms of x SUBSTITUTION 1: y=15-5x (15-5x)=25-5x 0=0 substitute x in terms of y SUBSTITUTION 2: y=15-5x therefore,5x=15-y y=25-(15-y) 2y=10 y=5 February 7th, 2010, 05:57 AM #5 Senior Member   Joined: May 2008 From: York, UK Posts: 1,300 Thanks: 0 Re: Linear Systems of Equations: Substition Method As long as there is a solution, you can always solve for either variable first. You have made an error in your second substitution: which is clearly false  Tags equations, linear, method, substition, systems Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post Akcope Calculus 3 March 14th, 2014 01:49 AM Jake_88 Linear Algebra 1 June 15th, 2010 05:59 AM MathMCMC Advanced Statistics 0 February 11th, 2010 11:43 AM maxpalme Algebra 1 April 2nd, 2009 10:33 AM maxpalme Abstract Algebra 1 December 31st, 1969 04:00 PM

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