SOLUTION: don't know why the substitution method my head wont engage in. I am a college student , this on is driving me crazy x+y=4,y=3x using substitution method. in need of serious help.

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Question 557977: don't know why the substitution method my head wont engage in. I am a college student , this on is driving me crazy x+y=4,y=3x using substitution method. in need of serious help.
Found 2 solutions by Alan3354, josmiceli:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
x+y=4,y=3x using substitution method.
---------
x+y=4
y=3x
-----
Sub for y in the 1st eqn, find x.
x + 3x = 4
4x = 4
x = 1
------
y = 3

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
A simple example of substitution is:
(1) +x+%2B+y+=+5+
(2) +y+=+3+%2B+x+
Substitute (2) into (1)
You can do this because +y+ appears
in both equations
(1) with the substitution is:
(1) +x+%2B+%28+3+%2B+x+%29+=+5+
(1) +2x+%2B+3+=+5+
(1) +2x+=+2+
(1) +x+=+1+
and, since
(2) +y+=+3+%2B+x+
(2) +y+=+3+%2B+1+
(2) +y+=+4+
-----------------
Here's your problem:
(1) +x+%2B+y+=+4+
(2) +y+=+3x+
I will substitute (2) into (1)
(1) +x+%2B+%28+3x+%29+=+4+
(1) +4x+=+4+
(1) +x+=+1+
and, since
(2) +y+=+3x+
(2) +y+=+3%2A1+
(2) +y+=+3+
So, the solution is the point (1,3)
Here's a plot of the lines
(1) +x+%2B+y+=+4+
(2) +y+=+3x+
+graph%28+400%2C+400%2C+-6%2C+6%2C+-6%2C+6%2C+-x+%2B+4%2C+3x+%29+