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Question :
Nilai dari Sin (pi / 14) x Sin (3pi / 14) x Sin (9pi / 14) adalah ...

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Answer 1

Verified answer

Sin(pi/14) = cos(6pi/14)
sin(3pi/14) = cos(4pi/14)
sin(9pi/14) = cos(2pi/14)

1/2sin2a = sinacosa

cosa.sinb = 1/2(sin(a+b) - sin(a+b))

cos(3pi/7).cos(2pi/7).cos(pi/7).sin(pi/7)/sin(pi/7)
1/2cos(3pi/7).cos(2pi/7).sin(2pi/7)/sin(pi/7)
1/4cos(3pi/7).sin(4pi/7)/sin(pi/7)
1/8(sin(pi)+sin(pi/7)/sin(pi/7)
1/8(0+sin(pi/7)/sin(pi/7)
1/8sin(pi/7)/sin(pi/7)
1/8

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