sin2x=2sinx cosx
cos2x=cos^2 (x)-sin^2 (x)
=2cos^2 (x)-1
=1-2sin^2 (x)
tan2x=2tanx/[1-tan^2 (x)]
(1)sin2x=2sinx cosx
(2) cos2x=(cosx)^2-(sinx)^2
(3)cos2x=2(cosx)^2-1
(4)cos2x=1-2(sinx)^2
(5)tan2x=2tanx/((1-tanx)^2)
(sinx)^2=1/2(1-cos2x)
(cosx)^2=1/2(1+cos2x)
sin2x=2sinx cosx
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