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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