An expression of the form a2−2ab+b2 can be factored to a perfect square. a2−2ab+b2=(a−b)2 An example is the expression x2−10x+25 which can be written as x2−2⋅x⋅5+52, and thus, be factored to the square of the binomial x−5. x2−2⋅x⋅5+52=(x−5)2