Question

Factor by grouping. a2 + ab – 56b2

Answer 1

a^2 + ab -56b^2
= a^2 +8ab -7ab -56b^2
= a (a+8b) -7b ( a+ 8b)
= (a-7b)(a+8b).

Answer 2

a^2 + ab - 56b^2

Factor by grouping is typically done when you have 4 terms not 3.
This is a trinomial that is factorable as is.
If it has to be done by grouping I can do that also. Let me know.

What are the factors of -56 that add up to 1?
8 * (-7) = -56
8 + (-7) = 1

(a + 8b)(a - 7b)