A perfect square is an expression in this form:
[tex](a+b)^2=a^2+2ab+b^2[/tex]
So, we have two perfect squares, and twice the product of the roots.
We have the two perfect squares: [tex]x^2[/tex] is the square of [tex]x[/tex], and 4 is the square of 2.
So, our perfect square can be completed in one of the two following ways:
[tex]x^2-4x+4 = (x-2)^2,\quad x^2+4x+4 = (x+2)^2[/tex]
