How do you factorise 7a2 -8ab?

To factorize the expression 7a^2 - 8ab, you need to find the greatest common factor of the two terms. In this case, the common factor is a. So, you can factor out an 'a' to get a(7a - 8b) as the factored form of the expression. This means that 7a^2 - 8ab can be simplified as a multiplied by the quantity (7a - 8b).