# Thread: How can I prove this inequality?

1. ## How can I prove this inequality?

Hey guys,
I've got a problem which shouldn't be too tricky, but for some reason I can't quite get it.2
I want to prove that x2-2xy+3y2>= 0
I can see that this is true because x2+3y2 will always be larger than 2xy, but I am not sure how to formalise it as a proof. This is something I often struggle with :\

2. ## Re: How can I prove this inequality?

$\displaystyle x^2-2xy+y^2+2y^2=(x-y)^2+2y^2 \geq 0$