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

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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 open parentheses 2 A close parentheses identical to 2 sin A cos A

    • cos left parenthesis 2 A right parenthesis identical to cos squared A minus sin squared A

      • cos left parenthesis 2 A right parenthesis identical to 2 cos squared A minus 1

      • cos left parenthesis 2 A right parenthesis identical to 1 minus 2 sin squared A

    • tan left parenthesis 2 A right parenthesis identical to fraction numerator 2 tan A over denominator 1 minus tan squared A end fraction

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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