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# Trignometry-sin3A

How can I write sinA in terms of sin3A?

Note by Naren Ezhil
2 years, 7 months ago

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I have to find sinA from the equation where no value for sin function is given.Like an equation in variable sinA

- 2 years, 7 months ago

Hint: State $$\sin(3A) = \sin(2A + A) = \sin(2A) \cos(A) + \cos(A) \sin(2A)$$. Use the double angle formula for $$\cos(2A)$$ and $$\sin(2A)$$ and apply the fundamental identity $$\sin^2(A) + \cos^2(A) = 1$$.

- 2 years, 7 months ago

What's the big difference if you write $$\sin (3A)$$ in terms of $$\sin (A)$$ or vice-versa ? All you will be needing is a relation between the two , and it is :

$$\sin (3A) = 3\sin (A) - 4\sin^{3} (A)$$

- 2 years, 7 months ago

- 2 years, 7 months ago

I got 341 .

- 2 years, 7 months ago