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| Math Central | Quandaries & Queries |
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Question from mike, a student: cos3A=-1/3 find cos6A thanks |
Hi Mike,
I would use the fact that sin2(x) + cos2(x) = 1 to find sin(3A). But 6A = 2 × 3A so do you know an expression for the cosine of twice an angle in terms of the sine and cosine of the angle?
Penny
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