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How do you find the exact value of #cos ((7pi)/12)#?

1 Answer

A. S. Adikesavan

May 27, 2016

Exactly # -(sqrt 3-1)/(2sqrt 2) =-0.25882#, nearly

Explanation:

#cos((7pi)/12)#

#=cos(pi/3+pi/4)#

#=cos (pi/3) cos (pi/4) - sin ((pi/3) sin (pi/4)#

#=(1/2)(1/sqrt 2)-(sqrt 3/2)(1/sqrt 2)#

#=-(sqrt 3-1)/(2 sqrt 2)#

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