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How do you verify #cos 2x = (1-tan^2x)/(1+tan^2x)# using the double angle identity?

1 Answer

Jul 21, 2016

#LHS=cos2x=cos(x+x)#

#=cosx*cosx-sinx*sinx#

#=(cos^2x-sin^2x)/(cos^2x+sin^2x)#

#=(cos^2x/cos^2x-sin^2x/cos^2x)/(cos^2x/cos^2x+sin^2x/cos^2x)#

#=(1-tan^2x)/(1+tan^2x)=RHS#

Verified

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