Final answer:
To factorise the expression 3a(x-y)-(x-y), identify (x-y) as the common factor and then express the equation as (x-y)(3a-1), which is the factorised form.
Step-by-step explanation:
The question requires us to factorise the expression 3a(x-y)-(x-y). The key to factorising this expression is to recognize that (x-y) is a common factor in both terms. Here is a step-by-step explanation of the factorisation process: