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Trigonometry - Further Identities (CIE A Level Maths: Pure 3)
Revision Note
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:
- tan2x + 1 ≡ sec2x
- 1 + cot2x ≡ cosec2x
- These are not really 'new' identities – they can both be derived from sin2x + cos2x ≡ 1
- To derive the identity for sec2x divide sin2x + cos2x ≡ 1 by cos2x
- To derive the identity for cosec2x divide sin2x + cos2x ≡ 1 by sin2x
Examiner Tip
- These identities are given in the exam formulae booklet – make sure you know how to find them.
- They will be needed to prove some trigonometric identities and solve some trigonometric equations.
Worked example
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