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Apr 1 2014 05:44am
2x + 3y + z = -3
x + 4y -3z = -23
3x - y +2x = 14


i've tried to solve it numerous times and keep coming up with decimals / fractions ? just want to make sure i'm not missing something or solving wrong

thanks in advance
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Apr 1 2014 06:09am
Quote (CFBI @ 1 Apr 2014 11:44)
2x + 3y + z = -3
x + 4y -3z = -23
3x - y +2x = 14 i assume it's 2z and not 2x as thrid variable
i've tried to solve it numerous times and keep coming up with decimals / fractions ? just want to make sure i'm not missing something or solving wrong
thanks in advance


first step is to take one of the variables from one of the equations and plug into the other two, so for starters

z = -3 - 2x - 3y

which creates the following two equations with 2 variables:

x + 4y - 3*(-3-2x-3y) = -23 and
3x - y + 2*(-3-2x-3y) = 14

now to simplify

x + 4y + 9 + 6x +9y = 7x +13y + 9 =-23 -> 7x+13y=-32
3x - y - 6 - 4x - 6y = -x - 7y- 6 = 14 -> x+7y=-20

now from the second x = -7y -20 which can be plugged into the other equation

7*(-7y-20)+13y=-32 -> -49y-20+13y=-32 -> -36y=-12 -> y=1/3

now you can plug this into the previous equation etc ... so, yes there are fractions
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Apr 1 2014 06:12am
Quote (CFBI @ Apr 1 2014 06:44am)
2x + 3y + z = -3
x + 4y -3z = -23
3x - y +2x = 14


i've tried to solve it numerous times and keep coming up with decimals / fractions ? just want to make sure i'm not missing something or solving wrong

thanks in advance


use substitution/elimination. if you need to double check your answer, simply plug in your [x, y, z] and see if they work. nothing wrong with fractions.
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Apr 1 2014 06:16pm
if you have a graphing utility, input your values into a matrix and find reduced row echelon form (rref)
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