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

3 Answers
Karthik N
May 1, 2018

x = -4x=−4
y = -8y=−8

Explanation:

We know that y = x - 4y=x−4. We also know that y = 2xy=2x

This must mean that x - 4 = 2xx−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−4=2x−x(subtracting x from both sides)
implies x = -4⇒x=−4

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

Manasvini Nittala
May 1, 2018

the value of xx is -4−4 and yy is -8−8

Explanation:

given equations are y=x-4 and y=2xy=x−4andy=2x
put y=2xy=2xin y=x-4 y=x−4 then we have 2x=x-4rArr2x-x=-4rArrx=-42x=x−4⇒2x−x=−4⇒x=−4 since y=2xrArry=-8y=2x⇒y=−8

Victor
May 1, 2018

x=-4 and y=-8x=−4andy=−8

Explanation:

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

Let's plug y=x-4y=x−4 into y=2xy=2x

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

Move variables to one side and constants in another

x-2x=4x−2x=4

-x=4−x=4

x=-4x=−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=-8y=x−4=(−4)−4=−8

y=2x=2(-4)=-8y=2x=2(−4)=−8

So, x=-4 and y=-8x=−4andy=−8

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