cos(派/2+a)-2sin(a-派/2)=0
sin(-a)-2cos(π-a)=0
-sina+2cosa=0
sina=2cosa
tana=2
sin^2a+sinacosa-2cos^2a
=(sin^2a+sinacosa-2cos^2a)/(sin^2a+cos^2a)
=(tan^2a+tana-2)/(tan^2a+1)
=(4+2-2)/(4+1)
=4/5
cos(派/2+a)-2sin(a-派/2)=0
sin(-a)-2cos(π-a)=0
-sina+2cosa=0
sina=2cosa
tana=2
sin^2a+sinacosa-2cos^2a
=(sin^2a+sinacosa-2cos^2a)/(sin^2a+cos^2a)
=(tan^2a+tana-2)/(tan^2a+1)
=(4+2-2)/(4+1)
=4/5