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

3 Answers
Karthik N
May 1, 2018

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)
⇒x=−4

Now we know that x=−4. y=2x must mean that y=2(−4)
⇒y=−8

Manasvini Nittala
May 1, 2018

the value of x is −4 and y is −8

Explanation:

given equations are y=x−4andy=2x
put y=2xin y=x−4 then we have 2x=x−4⇒2x−x=−4⇒x=−4 since y=2x⇒y=−8

Victor
May 1, 2018

x=−4andy=−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=−4andy=−8

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