tana=2,sina=2cosa,1-cos^2a=4cos^2a
cos^2a=1/5
(2sinα+cosα)/(sinα-cosα)
=5cosa/3cosa=5/3
sin^2α-2sinαcosa+cos^2α+2cos^2α
=1-4cos^2α+2cos^2α
=1-2cos^2α=3/5