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sin 2θ = 2 sinθcosθ 4pt
cos 2θ = 2 cos2θ - 1
tan 2θ = 2sinθ
8pt
You can uncover other multiple-angle formulas with Expand.
Following are some examples.
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sin 6θ = 32 sinθcos5θ -32 sinθcos3θ +6 sinθcosθ
sin 24θ = 8388608 sinθcos23θ - 46137344 sinθcos21θ
+ 110100480 sinθcos19θ - 149422080 sinθcos17θ
+ 127008768 sinθcos15θ - 70189056 sinθcos13θ
+ 25346048 sinθcos11θ - 5857280 sinθcos9θ
+ 823680 sinθcos7θ - 64064 sinθcos5θ
+ 2288 sinθcos3θ - 24 sinθcosθ
sin(2a + 3b) = 8 sin a cos a cos3b - 6 sin a cos a cos b
+ 8 cos2a sin b cos2b - 2 cos2a sin b
- 4 sin b cos2b + sin b