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Find all acute angles x such that cos(3x)*cos(x) + sin(3x)*sin(x) = cos(3*pi/5).

 Dec 28, 2019
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(cos (3x-x) ) = cos 3pi/5

cos 2x = cos 3pi/5

2x = 3 pi/5

x = 3pi/10

 Dec 28, 2019

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