左边=(tana/2 +1)/( 1- tana/2) + (tana/2 - )/( 1+ tana/2)=
=4*tana/2 /( 1- tan^2 a/2) = 2 tana
(2)1+cos2a+2sin^2a=2
左边=2cos^2a + 2sin^2a = 2 ( cos2a= 2cos^2a -1)