Extension maths can be surprisingly difficult for some people, mostly narrow minded people who follow everything there teacher tells them (don't hate me, I'm just saying).
Average students would do homework from primary till year 10 and when they get good marks they think they are geniuses and that they are talented at maths not realising that what they are studying is simply the very basics, that stuff is like below the basics. Then year 12 comes and their psyche gets pounded with extension 1 and 2 maths (which are a basic calculus + algebra course compared to the real shit).
What you have to do is:
1) Learn and understand the content by quickly going over the theory from a RELIABLE textbook, then do the entire exercise. In Terry Lee's textbooks, the entire exercise is relatively difficult (unlike Cambridge which gradually gets harder) so do ALL the questions. The way you should do the questions is by NOT looking at the solutions. What the fuck is the point of doing the exercise if you look at the solutions? Do the questions, keep trying until you get an answer then look at the solutions and NOTE down where you went wrong and understand how to do the question and hence formulate a structured way of thinking or a structured approach to solving the question. In the beginning just concentrate on improving your accuracy, not speed. Speed will be improved overtime as you practice more and more questions.
2) Now that you are done with learning the content start doing PAST PAPERS. Do not attempt questions that fall under topics you have not done yet, that is a waste of time. Do the questions in the past papers in the same way you do questions from the textbook "The way you should do the questions is by NOT looking at the solutions. What the fuck is the point of doing the exercise if you look at the solutions? Do the questions, keep trying until you get an answer then look at the solutions and NOTE down where you went wrong and understand how to do the question and hence formulate a structured way of thinking or a structured approach to solving the question. In the beginning just concentrate on improving your accuracy, not speed. Speed will be improved overtime as you practice more and more questions."
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