SOLUTION: please help. solve by substitution: y=2x x-y=4

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Question 43392: please help. solve by substitution: y=2x
x-y=4
Found 2 solutions by benni1013, psbhowmick:
Answer by benni1013(206) About Me  (Show Source):
You can put this solution on YOUR website!
y=2x
x-y=4
We know that y=2x so where y is in the second equation we put in 2x for y
x-2x=4==>-x=4==>x=-4

Answer by psbhowmick(878) About Me  (Show Source):
You can put this solution on YOUR website!
To solve the given equations by substitution, you have to replace one unknown (here, y) in one equation with its (that is y's) value in terms of the other unknown (here, x) from the other equation.

y = 2x ______(1)
x - y = 4 ____(2)

Replace 'y' in equation (2) with the value of 'y' from equation (1) in terms of 'x'.
Thus we get
x - (2x) = 4
or x - 2x = 4
or -x = 4
or x = -4

Now, put this value of 'x' (x = -4) in equation (1).
You get the value of 'y', y = 2x = 2(-4) = -8.

So the solution is x = -8, y = -4.