Quadratic simultaneous equation PLEASE help me

Question

nosnip · Answer

$$y= x-4$$
$$2x ^{2} -xy = 8$$
Give your answer in the form a±b sqrt(c)

welshfella · Answer

replace the y in the second equation by  x - 4 to form a quadratic in x

nosnip · Answer

It says I have to use elimination though?

nosnip · Answer

Should I make y the subject of both of them and then minus them?

hero · Answer

Multiply the first equation by x

hero · Answer

@nosnip

nosnip · Answer

So you get $$x ^{2} - xy - 4x = 0$$
$$2x ^{2} - xy - 8 = 0$$
Is that right?

nosnip · Answer

And then you have to minus them?

hero · Answer

What you want to do is setup the equations in a way where you can combine both together and eliminate the xy term . I try to setup to add rather than subtract

nosnip · Answer

So if the plus and minus signs were all reversed and x^2 and 2x^2 were both negative owuld that be better?

hero · Answer

attachment

nosnip · Answer

Got it thankyou so much :)

hero · Answer

What DID you get btw?

nosnip · Answer

Well it was a "prove that..." question and I got x^2 +4x - 8 which is what we had to prove so thanks :)

hero · Answer

I thought you had to solve for x in the form a±b sqrt(c)

nosnip · Answer

No that was a mistake I have to prove