How do you find exact value of sin (pi/ 3)?

1 Answer
Jul 24, 2016

sin (pi/3) = sqrt(3)/2

Explanation:

pi/3 Radians = 60 Degrees

sin 60 = sqrt(3)/2

To prove this consider an equilateral trigangle ABC of side 2 units as diagram below.

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The bisector of angle A meets side BC at D which is the midpoint of BC.

By Pythagoras:
AB^2 = AD^2 + DB^2
2^2 = AD^2 +1^2 -> AD = sqrt(4-1) = sqrt(3)

Angle B = 60 Degrees
Therefore: sin(60) = (AD)/(AB) = sqrt(3)/2