- Cosine Double Angle Formulae An animation (thinkwell.com)
- Exact Values 1 Some illustrative examples. Work out the exact values then click to see the steps. The tan examples are not relevant (mathsnet)
- Exact Values 2 Solve the examples, click to see the steps, then click again to generate a new example (mathsnet)
- Can you sort these jumbled proofs: Proof 1 , Proof 3 , Proof 4 ? (mathsnet)
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