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

1 Answer
Jul 18, 2016

sqrt3/2

Explanation:

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

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