# trig

posted by Steve

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

1. Reiny

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 75º
= cos(45 + 30)
= cos45cos30 - sin45sin30
= (√2/2)(√3/2) - √2/2)(1/2)
= (√6 - √2)/4

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