How do you factor 16a2 4b2?

Answer 1

Assuming the missing sign is "minus" then you have the difference between two squares.

This is solved as (x + y)(x - y).

In your example x = 4a and y = 2b so the factorisation is (4a + 2b)(4a - 2b) or more completely: (4)(2a + b)(2a - b).