This is the diference of 2 perfect squares. 4 is a perfect square, x^2 is a perfect square, and 25 is a perfect square. The pattern for this is (ax + b)(ax - b). Our a is 2 since 2*2 = 4, and our b is 5 since 5*5 = 25. So your factors are (2a+5)(2a-5), choice C.
