jacywilson14 said:
please help... i am completly lost
x+y-z=4
3x+2y+4z=17
-x+5y+z=8
You could solve the first equation for x in terms of y and z:
x + y - z = 4
x + y - z - y + z = 4 - y + z
x = 4 - y + z
Now, substitute (4 - y + z) for x in each of the remaining two equations.
Substituting into the second equation:
3x + 2y + 4z = 17
3(4 - y + z) + 2y + 4z = 17
12 - 3y + 3z + 2y + 4z = 17
-y + 4z = 5
<------there's ONE equation with just two variables
Substituting into the third equation:
-x + 5y + z = 8
-(4 - y + z) + 5y + z = 8
-4 + y - z + 5y + z = 8
-4 + 6y = 8
6y = 12
y = 2
And we've got the value of y! (It doesn't always work out so nicely!)
Now "back substitute"....you know what y is, so you can work with the equation that has just two variables, and find z.
And when you have the values for y and z, use one of the equations with three variables to find x.
