How do you solve the system #x=2y+7# and #x=y+4# using substitution?

1 Answer
Mar 18, 2017

Answer:

#y=-3# and #x=1#

Explanation:

We know #x=y+4# Plug that into #x=2y+7# for x:

#y+4=2y+7#

Move the #y# to one side by subtracting y on both sides:

#y+4-y=2y+7-y#

#4=y+7#

Subtract 7 on both sides:

#4-7=y+7-7#

#-3=y#

Personally, I like the y on the other side. You are allowed to flip the equation around:

#y=-3#

Now plug this in to one of the equations. I will plug it into the second equation:

#x=-3+4#

#x=1#

Check by plugging in to the other equation:

#1=2(-3)+7#

#1=-6+7#

#1=1#

It works out!