Evaluate cos 4π/3?

1 Answer
Yahia M.
Apr 26, 2018

#-1/2#

Explanation:

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

#=-cos(pi/3)# #color(green)(rarr"Using Quadrant sign for cosine function"#

#=-1/2#

Or you could do it with the Sum and Difference Identities

#cos(pi+pi/3)=cospi*cos(pi/3)-sinpi*sin(pi/3)#

#=(-1)(1/2)-(0)(sqrt3/2)=-1/2#

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