SOLUTION: My sons homework can not figure out Solve Systems of Equations Algebraically here is the question y=-x y=-7x can you show me how to get answer?

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Question 741070: My sons homework can not figure out Solve Systems of Equations Algebraically here is the question y=-x
y=-7x
can you show me how to get answer?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+y+=+-x+
+y+=+-7x+
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These are equations of straight lines which
intersect at some point
--------------------
It's a good idea to see what you can about the
lines, just by looking at the equations.
The general form of a straight line is
+y+=+m%2Ax+%2B+b+ where +m+ is the slope
of the lines. +b+=+0+ for both lines, so they
both look like +y+=+m%2Ax+
----------------------
+y+=+%28-1%29%2Ax+
The slope is +-1+
------------------
+y+=+-7x+
The slope is +-7+
-------------------
For the first equation, if I say
+x+=+0+, then:
+y+=+%28-1%29%2A0+
+y+=+0+
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For the 2nd equation, if I say
+x+=+0+, then
+y+=+%28-7%29%2A0+
+y+=+0+
---------------
I have just shown that both lines pass
through (0,0), which is the origin.
Two straight lines can only intersect at one point,
so, +x+=+0+, +y+=+0+ is the solution
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Here is the plot of the lines:
+graph%28+400%2C+400%2C+-8%2C+8%2C+-8%2C+8%2C+-x%2C+-7x+%29+