We have,

63a²b² – 7

= 7(9a²b² – 1)

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

We get,

63a²b² – 7 = 7(9a²b² – 1)

= 7{(3ab)² – (1)²}

= 7(3ab + 1)(3ab – 1)