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Trigonometry> Find the exact value of cos(13pi/12)...

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Find the exact value ofcos(13pi/12)

Kawal , 10 Years ago

Grade 11

2 Answers

Ranganna palem Srikanth

Last Activity: 10 Years ago

Exact answer of cos (13pi/12) is -1.833...... because cos (pi) is always -1

Jitender Singh

Last Activity: 10 Years ago

Ans:
Hello Student,
Please find answer to your question below

$A = cos(\frac{13\pi }{12})$
$A = cos(\pi +\frac{\pi }{12})$
$A = -cos(\frac{\pi }{12})$
$cos(\frac{\pi }{6}) = 2cos^{2}(\frac{\pi }{12}) - 1$
$2cos^{2}(\frac{\pi }{12}) = 1 + cos(\frac{\pi }{6})$
$cos(\frac{\pi }{12}) = \sqrt{\frac{1 + cos(\frac{\pi }{6})}{2}}$
$cos(\frac{\pi }{12}) = \sqrt{\frac{1 + \frac{\sqrt{3} }{2}}{2}}$
$cos(\frac{\pi }{12}) = \sqrt{\frac{2 + \sqrt{3}}{4}}$
$A = - cos(\frac{\pi }{12}) = -\sqrt{\frac{2 + \sqrt{3}}{4}}$

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