Value of cos 30°: Exact Form √3/2 & Decimal

How to derive it

In an equilateral triangle of side 2, drop a perpendicular: it splits into two 30°–60°–90° triangles with sides 1, √3 and 2.
cos = adjacent ÷ hypotenuse, so cos 30° = √3/2.

Angle	sin	cos	tan
15°	(√6 − √2)/4	(√6 + √2)/4	2 − √3
18°	(√5 − 1)/4	√(10 + 2√5)/4	√(25 − 10√5)/5
22.5°	√(2 − √2)/2	√(2 + √2)/2	√2 − 1
30°	1/2	√3/2	1/√3
36°	√(10 − 2√5)/4	(√5 + 1)/4	√(5 − 2√5)
45°	1/√2	1/√2	1
54°	(√5 + 1)/4	√(10 − 2√5)/4	√(25 + 10√5)/5
60°	√3/2	1/2	√3
67.5°	√(2 + √2)/2	√(2 − √2)/2	√2 + 1
72°	√(10 + 2√5)/4	(√5 − 1)/4	√(5 + 2√5)
75°	(√6 + √2)/4	(√6 − √2)/4	2 + √3

For whole-degree values from 0° to 90°, see the trigonometry table.

What is the value of cos 30°?

√3/2, which is about 0.8660.

What is cos 30° in radians?

30° is π/6 radians, so cos(π/6) = √3/2.

Is cos 30° equal to sin 60°?

Yes. cos θ = sin(90° − θ), so cos 30° = sin 60°.