Factor by grouping. a2 + ab - 56b2

a^2 + ab - 56b^2

= a^2 + 8ab - 7ab - 56b^2

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

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

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)