SOLUTION: 3x+9y=21 -8x=y=19 I am hoping to get some help with this, I am trying to solve by the substitution method, I am being told to solve the second equation first, but i do not unders

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Question 452224: 3x+9y=21
-8x=y=19
I am hoping to get some help with this, I am trying to solve by the substitution method, I am being told to solve the second equation first, but i do not understand why. Thank you so much for any help that you can give
Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
3x+9y=21
-8x+y=19
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You assume the x's mean the same in both
equations and the y's mean the same in
both equations.
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So you solve one of the equations for one of
the variables:
For example: y = 8x+19
-----
You substitute that expression into the other
equation in place of "y" to get an equation
with only the variable "x".
---
3x + 9*(8x+19) = 21
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Divide thru by 3 to get:
x + 3(8x+19) = 7
x + 24x + 57 = 7
25x = -50
x = -2
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Now you can solve for "y":
y = 8x+19
y = 8*(-2)+19
y = -16+19
y = 3
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Solution for the system of two equations: (-2,3)
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Cheers,
Stan H.
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