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November 28, 2014

November 28, 2014

Posted by **Amy** on Wednesday, December 23, 2009 at 7:12pm.

Thank you

- Pre-Cal -
**drwls**, Wednesday, December 23, 2009 at 9:16pmRemember that

cos(a+b) = cosa cosb - sina sinb

Therefore

cos5theta*cos 15 -sin5theta*sin 15

= squareroot of 3/2

cos(5theta + 15)

= cos^-1(sqrt3)/2

Take the arccosines of both sides

5 theta + 15 = 30 degrees5 theta = 15 degrees

theta = 3 degrees

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