Question

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

Answer 1

`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 2

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`

Answer 3

`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`