The expansion of a perfect square is
[tex] (a+b)^2 = a^2+2ab+b^2 [/tex]
In words, the square of a sum of two terms is the sum of the squares of the two terms ([tex] a^2[/tex] and [tex] b^2[/tex]), plus twice the product of the two terms ([tex] 2ab[/tex])
So, when determining if you have a perfect square trinomial, you should have two perfect squares. Note that they don't have to be the first and third term, since you can rearrange terms as you prefer.
