Factories:

25a² – 4b² + 28bc – 49c²

Given,

25a² – 4b² + 28bc – 49c²

= 25a² – (4b² – 28bc + 49c²)

By using the formula a² – b² = (a + b)(a – b)

We get,

25a² – 4b² + 28bc – 49c² = 25a² – (4b² – 28bc + 49c²)

= (5a)² – (2b – 7c)²

= {5a + (2b – 7c)}{5a – (2b – 7c)}

= (5a + 2b – 7c)(5a – 2b + 7c)