tan(45'+a)
=(tan45'+tana)/(1-tan45'tana)
=(1+tana)/(1-tana)=1/2
2+2tana=1-tana
tana=-1/3
tana=sina/cosa=-1/3
cosa=-3sina
(2sinacosa-cos^2a)/(2cos^2+sin^2a)
=(-6sin^2a-9sin^2a)/(18sin^2a+sin^2a)
=-15/19