How do you solve #y=x-4# and #y=2x# using substitution?

3 Answers
May 1, 2018

Answer:

#x = -4#
#y = -8#

Explanation:

We know that #y = x - 4#. We also know that #y = 2x#

This must mean that #x - 4 = 2x#. By 'substituting' y = 2x in the first equation, we have got a new equation in a single variable.
By solving,
#-4 = 2x - x#(subtracting x from both sides)
#implies x = -4#

Now we know that #x = -4#. #y = 2x# must mean that #y = 2(-4)#
#implies y = -8#

Answer:

the value of #x# is #-4# and #y# is #-8#

Explanation:

given equations are #y=x-4 and y=2x#
put #y=2x#in # y=x-4 # then we have #2x=x-4rArr2x-x=-4rArrx=-4# since #y=2xrArry=-8#

May 1, 2018

Answer:

#x=-4 and y=-8#

Explanation:

Substitution means plugging one equation to another to solve for a variable, so:

Let's plug #y=x-4# into #y=2x#

By plugging it in, you get #x-4=2x#

Move variables to one side and constants in another

#x-2x=4#

#-x=4#

#x=-4#

Since we found x, we can find y by plugging x back into either equations. Answer would be the same. To prove this, I'll plug x into both equations.

#y=x-4=(-4)-4=-8#

#y=2x=2(-4)=-8#

So, #x=-4 and y=-8#