tan(π/4+α)=k 求cos2α
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tan(π/4+α)=k 求cos2α
cos2α
=sin(Pi/2+2α)
=sin( 2(Pi/4+α) )
=2tan(π/4+α))/(1+tan^2(π/4+α))
=2k/(1+k^2)
tan(π/4+α)=k 求cos2α
cos2α
=sin(Pi/2+2α)
=sin( 2(Pi/4+α) )
=2tan(π/4+α))/(1+tan^2(π/4+α))
=2k/(1+k^2)