Yeah I find it easier too, but its recommended not to.
The reason is because in the guidelines, usually 1 mark is awarded for writing and substituting into one of the formulae, and another for the correct answer. Say you get your answer wrong or something, you'll still be able to get partial marks for substitution. But if you use 3u maths methods, you're not substituting into the given formulae and one mistake in calculation will get you a 0 regardless of the rest of your method
