IB DP Maths: AA SL复习笔记3.6.2 Double Angle Formulae
Double Angle Formulae
What are the double angle formulae?
- The double angle formulae for sine and cosine are:
These can be found in the formula booklet
-
- You do not need to know how to derive them
How are the double angle formulae used?
- Double angle formulae will often be used with…
- ... trigonometry exact values
- ... graphs of trigonometric functions
- ... relationships between trigonometric ratios
Solve
- The equation will most likely be in the form of a quadratic
- Double angle formulae can be used in proving other trigonometric identities
Exam Tip
- All these formulae are in the Topic 3: Geometry and Trigonometry section of the formula booklet
- If you are asked to show that one thing is identical (≡) to another, look at what parts are missing – for example, if sinθ has disappeared you may want to choose the equivalent expression for cos2θ that does not include sinθ
Worked Example
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