Question

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

Answer 1

`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!