Determine \sin(\frac{\pi}{14})+6\sin^2(\frac{\pi}{14})-8\sin^4(\frac{\pi}{14})

Cian Orr

Cian Orr

Answered question

2022-03-01

Determine
sin(π14)+6sin2(π14)8sin4(π14)

Answer & Explanation

Zernerqcw

Zernerqcw

Beginner2022-03-02Added 11 answers

A non-trivial result is that sinπ14 is a root to the equation
14x4x2+8x3=0
If you believe this, then you can simply apply polynomial division to obtain
x+6x28x4=(x+12)(8x34x24x+1)+12
So then, filling in x=sinπ14 gives you the answer:
sinπ14+6sin2π148sin4π14=12

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