Is there another way to do this? This way isn't very intuitive.
The short answer is no. The explanation given here is by far the most efficient and realistic solution to this question.
Now, that doesn't mean it's the most intuitive! The truth is that explanations to hard questions like this might be difficult to understand at first, but that's exactly why we're studying them! With time and practice, methods like this one--considering the effects of different values for the variables--will become more natural :-)