You can get to Core 4 comfortably, only every using equations with a couple of variables in. In C4, you suddenly get parametric equations thrown at you.
Once you adjust your mind to see what's going on, they're not that much more difficult than - say - implicit differentiation, but they can be confusing at first.
This book shows you how to master: * Finding points on a parametric curve; * Finding gradients, tangents and normals for parametric equations; * Integrating parametric equations to find areas and volumes;
... as well as loads of practical advice on how to tackle parametric equation questions.