# Deriving Trigonometric Formulae

You know what really grinds my gears??

You’re a diligent student…you know that you have to learn your proofs, theorems, constructions etc for a few guaranteed marks on the exam. You read the syllabus and it says “YOU MUST BE ABLE TO DERIVE THE TRIGONOMETRIC FORMULAE 1,2,3,4,5,6,7,9″….
You learn them all off by heart…go into the exam…and get asked FORMULA 10!!

Now it is just a case of taking Formula 9 and changing the B to a -B…but that is also the case with formulae 3 and 4, both of which are on the learn off list above…and my issue is more that it causes confusion on the day for a good student. They’ll be questioning did they miss one of the formulae they were to learn off OR did the teacher give them the right proofs to learn.

It was asked so that they can ask the part (ii) of the question…which I might post in a bit. It’s the sort of question that was asked 20 years ago…and I think you’d have to go back Pre-2000 to see a question like it!

These Trig Identity questions made very little appearance when the new syllabus first came in but are becoming more and more frequent, to the point that they need to be revised as much as solving triangles type trigonometry questions.

Subscribers can find the following LCHL Trigonometry content in the folders.

1. Trigonometry Revision Sheet
2. Trigonometric Proofs Pack
3. Trigonometric Functions – Real World Context
4. Trigonometric Functions and Graphs – No Real World Context
5. Trigonometry – Equations and Identities
6. Trigonometry – Solving Triangles

and in the EXTRA resources folder…
7. Trigonometry – Identities and Equations EXTRA
8. Trigonometry – Sectors and Arcs
9. Trigonometry – Solving Triangles EXTRA
10. Trigonometry – Trigonometric Equations