This wouldn't be as relevant to you as there is no calculus in Standard Math (I believe ... could be wrong), but with these types of questions, you're definitely able to use any method you are comfortable with. Just make sure as it's 3 marks, you show sufficient working out and your steps are logical. With some integration questions for example, they may directly tell you to use a specific method (substitution or partial fractions, you don't have to worry about that). I was just going to say with questions like that, it's crucial you use the method they give you, because this tests if you understand the entire syllabus.