SOLUTION: My question is whats substition I keep hearing about? How does it work? Can you tell me how to solve a problem using substition?

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Question 529648: My question is whats substition I keep hearing about? How does it work? Can you tell me how to solve a problem using substition?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Sure.
Suppose you have 2 equations with
2 unknowns. It definitely should be
solvable, and one way is by substitution.
Say the equations are
(1) +x+-+y+=+10+
(2) +3x%5E2+%2B+9y%5E2+=+300+
-----------------------
From(1), I get
(1) +x+=+y+%2B+10+
Now I will Substitute this value of x
into equation (2)
(2) +3%2A%28+y+%2B+10+%29%5E2+%2B+9y%5E2+=+300+
(2) +3%2A%28+y%5E2+%2B+20y+%2B+100%29+%2B+9y%5E2+=+300+
(2) +3y%5E2+%2B+60y+%2B+300+%2B+9y%5E2+=+300+
(2) +12y%5E2+%2B+60y+=+0+
(2) +12y%2A%28y+%2B+5%29+=+0+
+y+=+0+
+y+=+-5+
The solutions are
(10,0) and (5,-5)