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Suppose $\cos\theta=0,7$. Find $\cos 2\theta$ and $\cos 4\theta$
in Grade 12 Maths by Bronze Status (5.9k points) | 26 views

1 Answer

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use double angle identity

cos2x= 2cosx^2 -1= 2.(0.7)^2 - 1= -0.02

cos4x= cos2.(2x)= 2cos (2x)^2 -1= 2.(1.4)^2 - 1= 2.92
by Diamond (82.9k points)

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