Question #a451b

1 Answer
ali ergin
Jun 15, 2017

cos(210)=-sqrt3 /2

Explanation:

cos (210)=cos (180+30)
cos(a+b)=cos a*cos b-sin a*sin b
cos(210)=cos(180)*cos(30)-sin(180)*sin(30)
cos(180)=-1
cos(30)=sqrt 3/2
sin(180)=0
sin(30)=1/2
cos(210)=cos(180)*cos(30)-sin(180)*sin(30)
cos(210)=-1*sqrt 3/2-0*1/2
cos(210)=-sqrt 3/2-0
cos(210)=-sqrt3 /2

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