find cos 20 if cos theta equal to 2√2/3

find cos 20 if cos theta equal to 2√2/3
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You mean cos(2θ)?

cos(2θ)=2cos2θ-1=2(2√2/3)2-1=2(8/9)-1=16/9-1=16/9-9/9=7/9.

cos(2θ)=7/9.

by Top Rated User (1.1m points)

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