Having trouble factoring a^2 - ab - 2b^2

Just be in love with the expression first.

a^2 - ab - 2b^2. Replace - ab with = ab - 2ab

a^2 + ab-2ab - 2b^2 Factorize like terms.

a (a+b) - 2b (a+b) Factorize common terms:

= (a+b) (a-2b)

That's it, so you see, we didn't have trouble factorizing it, because we first fell in love with it.

A² - ab - 2b²

= a² - 2ab + ab - 2b²

= a (a - 2b) + b (a - 2b)

= (a - 2b) (a + b)