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 January 20th, 2009, 02:13 PM #1 Newbie   Joined: Jan 2009 Posts: 7 Thanks: 0 System of 3 equations with 3 variables Ok so here's the problem, and I tried to look up a way to do this but I am more confused than when i started. Find a quadratic function that fits the data on the right. The 3 points given are (20,20) (40,105) & (60,295) Using the points I can input into the quadratic model and get: 20= 400A+20B+C 105= 1600A+40B+C 295= 3600A+60B+C After this is where I'm lost and seriously need help. Can someone please help me work this and explain it in a way that makes some kind of sense? January 20th, 2009, 02:23 PM #2 Senior Member   Joined: Jul 2008 Posts: 895 Thanks: 0 Re: System of 3 equations with 3 variables Google: Solve three equations January 20th, 2009, 05:26 PM   #3
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Re: System of 3 equations with 3 variables

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 Originally Posted by 500lbgorilla I tried to look up a way to do this but I am more confused than when i started. January 21st, 2009, 08:59 AM #4 Global Moderator   Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,958 Thanks: 1146 Math Focus: Elementary mathematics and beyond Re: System of 3 equations with 3 variables The idea is to multiply the given equations by a factor that produces a common (equal) term which we can then eliminate from the equations using subtraction. Multiply Eq1 by 2 to get Multiply Eq1 by 3 to get Subtract Eq4 from Eq2 to get Subtract Eq5 from Eq3 to get Now, with Eq6 and Eq7, we have a system of two equations in two variables. Multiply Eq6 by 2 to get Subtract this from Eq7 and we get So A = 21/160, sub this into Eq6 getting Solve for C, C = 40. Since A = 21/160 and C = 40, it follows that B = -29/8 so our quadratic equation is January 24th, 2009, 07:59 AM #5 Global Moderator   Joined: Dec 2006 Posts: 20,926 Thanks: 2205 Eq3 - Eq2 gives Eq4: 2000A + 20B = 190. Eq2 - Eq1 gives Eq5: 1200A + 20B = 85. Eq4 - Eq5 gives 800A = 105, so A = 21/160. Eq3 - 3*Eq5 gives C = 295 - 3(85) = 40. 5*Eq5 - 3*Eq4 gives 40B = 425 - 570, so B = -29/8. Tags equations, system, variables 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 nicnicman Linear Algebra 4 October 22nd, 2013 02:27 AM BenderRR Calculus 0 April 4th, 2013 04:41 AM ZeusTheMunja Linear Algebra 20 January 25th, 2013 05:52 AM Russell368 Elementary Math 35 July 10th, 2011 08:32 PM morning_mood Algebra 6 December 21st, 2007 12:02 AM

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