Question 814634: Solve by substitution 3x+2y=12
x+y=3. How do I do this
Answer by LinnW(1048)   (Show Source):
You can put this solution on YOUR website! Solve one of the equations for either x or y in relation to the other.
For example:
x+y=3
Subtract y from each side
x=-y+3
Now we can substitute -y+3 for x in the other equation, so
3x+2y=12 becomes
3(-y+3) + 2y = 12
-3y + 9 + 2y = 12
-y + 9 = 12
Subtract 9 from each side
-y = 12 -9
-y = 3
Multiply each side by -1
-1(-y) = -1(3)
y = -3
To find the value of x, use our equation x=-y+3
x= -(-3)+3
x= 3 + 3
x=6
So we have y = -3 and x = 6
Check these values in the original equations.
3x+2y=12, doing the substitution
3(6)+2(-3)=12
18 -6 =12 , so the first equation checks out.
x+y=3
6+(-3)=3
6-3=3, so the second equation checks out.
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