ASMathsCambridge (CIE)Pure 2Revision NotesTrigonometryCompound & Double Angle FormulaeDouble Angle Formulae

Double Angle Formulae (Cambridge (CIE) AS Maths: Pure 2): Revision Note

Exam code: 9709

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Double angle formulae

What are the double angle formulae?

The double angle formulae are derived from the 'A+B' versions of the compound angle formulae:
- $\sin (2 A) \equiv 2 \sin A \cos A$
- $\cos (2 A) \equiv \cos^{2} A - \sin^{2} A$
  - $\cos (2 A) \equiv 2 \cos^{2} A - 1$
  - $\cos (2 A) \equiv 1 - 2 \sin^{2} A$
- $\tan (2 A) \equiv \frac{2 \tan A}{1 - \tan^{2} A}$

Double Angle Forms Illustr 1_sin, A Level & AS Maths: Pure revision notes

Double Angle Forms Illustr 2_cos, A Level & AS Maths: Pure revision notes

Double Angle Forms Illustr 3_tan, A Level & AS Maths: Pure revision notes

Examiner Tips and Tricks

The double angle formulae can be found in the formulae booklet – make sure you know where to find them.
Look out for problems containing sinAcosA or an equation that contains both a double angle and a single angle.

Worked Example

Double Angle Forms Example, A Level & AS Maths: Pure revision notes

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