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If $\sin\theta=\frac{4}{7}$, again find $\cos 2\theta$ and $\cos 4\theta$
in Grade 12 Maths by Bronze Status (5.9k points) | 16 views

1 Answer

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use double angle identity

cos2x= 1-2sinx^2= 1-2.(4/7)^2= 0.35

cos4x= cos2.(2x)= 1- 2sin(2x)^2= 1- 2.(2x4/7)^2 = -1.61
by Diamond (82.9k points)

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