How do you find the value of cos ((13pi)/12)?

1 Answer
P dilip_k
May 7, 2016

=-1/2sqrt(1/2(sqrt3+1))

Explanation:

cos((13pi)/12)=cos(pi+pi/12)=-cos((pi)/12)
=-sqrt(1/2(1+cos(2*pi/12)))=-sqrt(1/2(1+cos(pi/6)))
=-sqrt(1/2(1+sqrt3/2))=-sqrt(1/8(4+2*sqrt3))
=-sqrt(1/(2*2^2)((sqrt3)^2+2*sqrt3*1+1^2))
=-sqrt(1/(2*2^2)(sqrt3+1)^2)

=-1/2sqrt(1/2(sqrt3+1))

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