Question 630636
4x^2- 20xy +25y^2

this is a perfect square trinomial

4x^2 = (2x)^2; 25y^2 = (5y)^2

Factoring:

4x^2- 20xy +25y^2

(2x - 5y)(2x - 5y) = (2x - 5y)^2

Check, expand the binomial squared (using FOIL):

(2x - 5y)(2x - 5y) = 4x^2 - 10xy - 10xy + 25y^2 = 4x^2- 20xy +25y^2