How do you verify the identity #-2cos^2theta=sin^4theta-cos^4theta-1#?

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Answer 1 · 2016-10-07T16:10:09

see below bolded text

#-2cos ^2 theta=sin^4 theta-cos^4theta-1#

Right Side : #=sin^4 theta-cos^4theta-1#

#=(sin^2theta-cos^2theta)(sin^2theta+cos^2theta)-1#

#=(sin^2theta-cos^2theta) *1 - 1#

#=sin^2theta-cos^2theta-1#

#=1-cos^2theta-cos^2theta-1#

#=cancel1-2cos^2theta-cancel 1#

#=-2cos^2theta#

#:.=# Left Side