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January 31, 2015

January 31, 2015

Posted by **Lauren** on Sunday, November 13, 2011 at 3:23pm.

- Trig -
**Reiny**, Sunday, November 13, 2011 at 3:58pmsometimes I find it easier to visualize these kind of angles in degrees

π/12 radians = 15°,

so -11π/12 = -165°

and 165 = 120+45

cos(-11π/12) = cos(-165° = cos(165°)

= cos(120 + 45)

= cos120cos45 - sin120sin45

= (-1/2)(1/√2) - (√3/2)(1/√2)

= (-1 - √3)/(2√2)

or

= (-√2 - √6)/4

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