Edexcel A Level Maths: Pure:复习笔记5.5.3 Trigonometry - Further Identities
Trigonometry - Further Identities
What identities do I need to know with secant, cosecant, and cotangent?
- There are two identities with sec, cosec and cot that you need to know and be able to use:
- These are not really 'new' identities – they can both be derived from sin2x + cos2x ≡ 1
Exam Tip
- These identities are not given in the exam formulae booklet – you have to know them.
- If you forget them (or forget where the '+1' goes) you can always derive them from sin2x + cos2x ≡ 1 as shown above.
- Unless told otherwise, you can assume sin2x + cos2x ≡ 1 in any proofs involving sec, cosec or cot on the exam.
Worked Example
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