Home/Question #1953
PracticeMedium

Q.The sum of 20 terms of the series cos⁡α+(cos⁡αcos⁡β+sin⁡αsin⁡β)+(cos⁡αcos⁡2β+sin⁡αsin⁡2β)+⋯\cos \alpha + (\cos \alpha \cos \beta + \sin \alpha \sin \beta) + (\cos \alpha \cos 2\beta + \sin \alpha \sin 2\beta) + \cdots is

a
sin⁡10βsin⁡βcos⁡(α+9β)\dfrac{\sin 10\beta}{\sin \beta} \cos (\alpha + 9\beta)
b
sin⁡20βsin⁡βcos⁡(α+9β)\dfrac{\sin 20\beta}{\sin \beta} \cos (\alpha + 9\beta)
c
sin⁡10β2sin⁡βcos⁡(α+9β)\dfrac{\sin 10\beta}{2\sin \beta} \cos (\alpha + 9\beta)
d
sin⁡20β2sin⁡βcos⁡(α+10β)\dfrac{\sin 20\beta}{2\sin \beta} \cos (\alpha + 10\beta)

Correct Answer: Option C

The correct solution involves applying the fundamental concept to derive the final value step by step...

Unlock Detailed Solution

Register for Free

Already a member? Login here