Many students have a hard time with trigonometric identities, especially in Grade 9 Pre-Calculus. Here are some common mistakes they make:

1. Confusing Identities: Students often mix up the basic identities. A big one is the Pythagorean identity. For example, they might think that if $sin^2(x) + cos^2(x) = 1$, then it means $sin^2(x) = 1$ when $cos^2(x) = 0$. This kind of misunderstanding can lead to big mistakes when proving ideas or simplifying problems.

2. Using Reciprocals Wrongly: Sometimes, students struggle with reciprocal identities. They might forget that $csc(x) = \frac{1}{sin(x)}$ and accidentally treat it like $\frac{1}{sin^2(x)}$. This can lead to wrong answers in their calculations.

3. Ignoring Domain Restrictions: Many students don’t think about the domain and range of trigonometric functions. Not considering these can mess up their results, especially in quotient identities where dividing by zero can happen.

To fix these problems, regular practice is super important. Using visual aids can help make the ideas clearer. Students should do a lot of practice problems, double-check their definitions, and get to know the graphs of trigonometric functions better. Working with friends can also help clear up any confusion, which will help build their confidence in using trigonometric identities.