
Algebra PreAlgebra and Basic Algebra Math Forum 
 LinkBack  Thread Tools  Display Modes 
January 6th, 2017, 08:15 PM  #1 
Senior Member Joined: Jan 2017 From: US Posts: 104 Thanks: 5  Which Method Should I use to Solve this System of Equations?
x + y = 4 y = 3x I am not sure which method I should use for this system of equations. I could use the addition method, but there are't any numbers aside from 4 in the first equation, and the same would happen when using the elimination method, so how would that work? I can use either the addition method, the elimination method, the substitution method or the graphing method. Just looking at this, I have determined the ordered pair (1,3) to be the solution, but that is without using a particular "method" which is what I am supposed to do. Any help would be appreciated! Thanks Last edited by Indigo28; January 6th, 2017 at 08:22 PM. 
January 6th, 2017, 08:26 PM  #2 
Senior Member Joined: Feb 2016 From: Australia Posts: 1,579 Thanks: 541 Math Focus: Yet to find out. 
Substitution looks easiest, but maybe you solved it intuitively, without really thinking about which method you used This can be a good sign of your understanding! It's given that y = 3x in the second equation, so just substitute your expression for y in the first equation; x + 3x = 4 4x = 4 x = 1. Now you know what x is, substitute it back into the second equation! y = 3(1) = 3. Looks to me like your answer is correct. 
January 6th, 2017, 08:30 PM  #3  
Senior Member Joined: Jan 2017 From: US Posts: 104 Thanks: 5  Quote:
Wow that looks a lot more simple than I made it out to be lol. Thank you!  
January 6th, 2017, 08:32 PM  #4 
Senior Member Joined: Feb 2016 From: Australia Posts: 1,579 Thanks: 541 Math Focus: Yet to find out.  
January 7th, 2017, 04:36 AM  #5 
Global Moderator Joined: Dec 2006 Posts: 18,847 Thanks: 1568 
x + y = 4 3x  y = 0 Adding those eliminates y, giving 4x = 4, so x = 1. It's now possible to find y by substituting 1 for x in either equation. Alternatively, multiplying the first equation by 3 gives 3x + 3y = 12. Subtracting the second equation from that gives 4y = 12, so y =3. 

Tags 
equations, method, solve, system 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Solve the system of equations by the elimination method  GIjoefan1976  Algebra  3  April 21st, 2016 08:15 PM 
Solve each system by the substitution method.  nightotter  Algebra  4  June 18th, 2014 11:49 AM 
Use the echelon method to solve the following system of two  niaboc  Algebra  3  October 1st, 2012 03:36 PM 
Solve a system of equations?  Axle12693  Algebra  2  January 22nd, 2010 07:41 PM 
Newton's method, system of nonlinear equations  EoA  Computer Science  5  April 19th, 2008 09:54 AM 