How do you find the value of cos (pi)/6?

sqrt3/2

There are 2 ways, that don't need calculator a. Trig table of special arc --> ##cos (pi/6) = sqrt3/2## b. Use triangle trigonometry Consider a right triangle ABH that is half of an equilateral triangle ABC Angle ##A = pi/6 = 30^@##, Angle ##B = 60^@##, Angle ##H = 90^@## Leg ##AH = sqrt3##; Leg BH = 1, Hypotenuse AB = 2. We have ##cos A = cos (pi/6) = (AH)/(AB) = sqrt3/2##

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Edit from r3ce:

I believe another option to also look at especially for precalculus if it's applicable is the unit circle. It's basically a picture of certain common values for sine and cosine for angles such as ##pi/6## or ##(2pi)/3##