Expert: Paul Klarreich - 11/17/2008

Question
Hi, I am in solving systems of equation in three variables part of my chapter and I am having trouble with solving these three problems using the substitution method. Help?
Problem 1: 2b-6=-13
          2a=12
          3a+b=13
Problem 2: b+c=4
          2a+4b-c=-3
          3b=-3
Problem 3: r-s+3t=-8
          2s-t=15
          3r+2t=-7

Answer
Questioner:   Ashton
Category:  Advanced Math
Private:  No
 
Subject:  Solving Systems of Equation in Three Variables
Question:  Hi, I am in solving systems of equation in three variables part of my chapter and I am having trouble with solving these three problems using the substitution method. Help?
Hi, Ashton,

Problem 1: 2b-6=-13
         2a=12
         3a+b=13

You have only two variables here.  I think you mistyped.  Fix it.

..................
Problem 2: b+c=4
         2a+4b-c=-3
         3b=-3

I think you start with the last.  It gives you b = -1.  Then put that into the first equation to get c, then put THOSE into the second to get a.



Problem 3: r-s+3t=-8
         2s-t=15
         3r+2t=-7

I sugggest starting with the second.  [Strategy: look for the simplest equation, look for a variable with a coefficient of +-1.]a

2s = t + 15

t = 2s - 15.

Now put that into the others to get two equations in two variables.  You can take it from there.