What is #cos(2arccos0.25)#?

Mar 12, 2017

#cos(2arccos0.25)=-0.875#

Let #arccos0.25=x#, then #cosx=0.25#

Hence, #cos(2arccos0.25)#

#=cos(2x)#

#=2cos^2x-1#

#=2xx(0.25)^2-1#

#=2xx0.0625-1#

#=0.125-1#

#=-0.875#

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