Where have I gone wrong?

\frac{cos\theta - isin\theta}{({cos2\theta - isin 2\theta})^3} = \frac{cos(-\theta) + isin(-\theta)}{cos( -6\theta) + isin (-6\theta)}= cos(5\theta) + isin(5\theta)

Original post by NotNotBatman

\frac{cos\theta - isin\theta}{({cos2\theta - isin 2\theta})^3} = \frac{cos(-\theta) + isin(-\theta)}{cos( -6\theta) + isin (-6\theta)}= cos(5\theta) + isin(5\theta)

It's correct.

It's correct.

The book has the answer as

cos(5\theta) - isin(5\theta)

, just a mistake?

Original post by NotNotBatman

The book has the answer as

cos(5\theta) - isin(5\theta)

, just a mistake?

Yes. You can check the answer with a calc on your complex mode for any angle.

Yes. You can check the answer with a calc on your complex mode for any angle.

Thanks.

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