When you have four terms: factor by grouping; two terms at a time. However, in this equations, you must know the formula for the difference of two squares:
a^2-b^2=(a+b)(a-b)
(a+b)(a-b)+5(a+b): note on each side of the operation (the plus sign "+") there is an (a+b) in common. Factor the like terms; in this case (a+b)...therefore,
(a+b)[(a-b)+5]