Respuesta :

25x^4-16y^2 is the difference of 2 squares:  (5x^2)^2 - (4y)^2

Recall that a^2 - b^2 = (a-b)(a+b).

Here,  
(5x^2 - 2y)(5x^2 + 2y)   (answer)
The answer is (5x^2+4y)(5x^2-4y)