Trigonometry Angles--Pi/6 -- from Wolfram MathWorld
Ex: Sine and Cosine Values Using the Unit Circle - Multiples of pi/6 radians - YouTube
Working with Multiples of pi/6, pi/4, and pi/3 - YouTube
Trig values of π/6, π/4, and π/3 (practice) | Khan Academy
Trigonometry Angles--Pi/6 -- from Wolfram MathWorld
Find the Exact Value of the Secant of (5*Pi/6) Using the Unit Circle - YouTube
Basel problem - Wikipedia
Values of trigonometric functions of arcs pi/6 pi/4 and p/3, The values of the trigonometric functions of arcs that are multipliers of 30 degrees (pi/6) and 45 degrees (pi/4