No, in a perfect world (or any world for that matter), (x-y)(x+y) = xx - yy 

Wedge of Cheese said:reread this:Wedge of Cheese said:If you look at C# and Eb on a keyboard, you'll see that they are 2 half steps apart, which might lead you to say that the interval is a M2. However, you would be incorrect if you said that. The way you would go about figuring out the correct answer would be to first ignore any sharps or flats in the notes (i.e. just think "C" and "E"). Take these two notes, and count the white keys from one to the other (including the notes themselves). There are 3 white keys in this range (C, D, and E). This tells you that the interval must be some kind of a third.