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If cos x=8/17 and 270° < x < 360° what is cos(2x)⁡?
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3 votes
If cos x=8/17
and 270° < x < 360°
what is cos(2x)⁡?

User Chares
by
5.2k points

1 Answer

2 votes

It follows immediately from the double angle identity:


\cos2x=2\cos^2x-1=-(161)/(289)

User Stephen Lead
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