Simplify (3y)^2 + x^2 - (2y)^2, I answered 5y^2+x^2 why did my teacher say my answer was wrong?

Question

Simplify (3y)^2 + x^2 - (2y)^2, I answered 5y^2+x^2 why did my teacher say my  answer was wrong?

luffingsails · Answer

$$(3y)^2 + x^2 - (2y)^2 = 9y^2 + x^2 - 4y^2 = 5y^2 + x^2$$

So, I am not sure why the teacher would say that.

anonymous · Answer

she said some poppywingspan about the terms not being mixed up

luffingsails · Answer

Well, as written, the answer you provided is correct. Unless you transposed the problem when re-writing it? <shaking head> Not sure.

anonymous · Answer

and that x^2+5y^2 is the right answer and if I put 5y^2+x^2 in an exam I would receive no marks

luffingsails · Answer

Ahh... well, that's a junk answer. Why should the x variable come before the y? Just because of the alphabet?

Sorry, some teachers are just nitwits.

anonymous · Answer

lol