Posted by **Steve** on Wednesday, December 16, 2009 at 9:57pm.

Use a half-angle formula to find the exact value of cos 5ð/12

- trig -
**Reiny**, Wednesday, December 16, 2009 at 10:11pm
your symbol for pi did not come out, just type pi, that seems to be the simplest way.

A lot of students seem to find it easier to think in degrees,

5pi/12 = 75º

cos(5pi/12) radians

= cos 75º

= cos(45 + 30)

= cos45cos30 - sin45sin30

= (√2/2)(√3/2) - √2/2)(1/2)

= (√6 - √2)/4

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