Sorry guys for posting such basic question but I can't find it anywhere.

How fo you recognize a quadratic equation? I know about counting the degree and stuff but is there maybe a test that can be done to test each equation?

Like for example: 7x+4xy-2x+5y Is this a quadratic?

Oh and someone told me that xy=6 is also a quadratic...how is that? Because of degree?

THanks guys

Derg