tana=3 则 sin²a+sin2a+2cos²a=

tana=3 则 sin²a+sin2a+2cos²a=
tana=3 则 sin²a+sin2a+2cos²a=

tana=3 则 sin²a+sin2a+2cos²a=
tana=sina/cosa=3,sina=3cosa
sin^2a+cos^2a=1
(3cosa)^2+cos^2a=1
cos^2a=1/10,sin^2a=9/10,tana=3>0,则sina与cosa同号,sinacosa=3/10
sin^2a+sin2a+2cos^2a
=sin^2a+2sinacosa+2cos^2a
=9/10+2*(3/10)+2*(1/10)
=17/10