djkenk linear equations!?

Question

Im having the absolute most difficult time understanding this.
..Using the substitution method to solve the linear system..
y=x + 3
3x - y =5 or this


3x = 9
-2x+ y= -8

I dont want the answers I just want to understand how to do it!! Please help i would really appreciate it

Answer 1

The first equation says that y is equal to x plus 3.
The second equation is more complicated, it relates x and y to 5.
So you take the simpler equation and plug it into the more complicated one.
That is, you replace the "y" in the second equation with its equivalent, "x+3" from the first one and get
3x - (x + 3) = 5
Then you simplify
2x - 3 = 5
Then you solve
2x = 8
x = 4
Finally you take this result and plug it into the simpler equation
y = x + 3
y = 4+ 3
y = 7
Now you have a pair of numbers that works in both equations.
3(4) - 7 = 5
There's explanations online that explain it a lot better than writing it here.
To find tutorials on any subject put tutorial subject in your search window. When I put tutorial linear equations substitution I got links like this...
http://www.wtamu.edu/academic/anns/mps/math/mathlab/int_algebra/int_alg_tut19_systwo.htm
http://www.sparknotes.com/math/algebra1/systemsofequations/section2.rhtml
http://www.sosmath.com/soe/SE2001/SE2001.html

Answer 2

Since you know what y equals plug it in. 3x - (x +3) = 5

You're plugging in the Y equation for y in teh second equation. Solve for X then plug it into Y. You might have to rearrange an equation to make it X = or y = and so forth.

Answer 3

Solve for one variable by plugging it into the other eq. Then plug that back into either eq. and solve.