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

1 Answer
Bdub
Mar 30, 2016

cos (pi/12)=sqrt6/4+sqrt2/4

Explanation:

cos (pi/12)=cos(pi/4 -pi/6)
cos(A-B)=cosAcosB+sinAsinB
cos(pi/4 -pi/6)=cos (pi/4)cos(pi/6)+sin(pi/4)sin(pi/6)
cos(pi/4 -pi/6)=sqrt2/2*sqrt3/2+sqrt2/2*1/2=sqrt6/4+sqrt2/4
cos (pi/12)=sqrt6/4+sqrt2/4

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