How do I find the value of csc pi/12?

1 Answer
Aug 12, 2015

Find csc (pi/12)

Ans: 2/sqrt(2 - sqrt3)

Explanation:

csc (pi/12) = 1/sin (pi/12). Find sin (pi/12)
call sin (pi/12) = sin t
cos 2t = cos ((2pi)/12) = cos ((pi)/6) = sqrt3/2.
Use trig identity: cos 2t = sqrt3/2 = 1 - 2sin^2 t
2sin^2 t = 1 - sqrt3/2 --> sin^2 t = (2 - sqrt3)/4
sin (pi/12) = sin t = +- sqrt(2 - sqrt3)/2
Since sin (pi/12) is in Quadrant I, therefor, only the positive answer is accepted.

csc (pi/12) = 2/(sqrt(2 - sqrt3)