cosa+2sina=-√5cosa=-√5-2sinacosa=-√5-2sina代入(cosa)^2+(sina)^2=1(-√5-2sina)^2+(sina)^2=15(sina)^2+4√5sina+4=0(√5sina+2)^2=0sina=-2/√5cosa=-√5-2sina=-1/√5tana=sina/cosa=(-2/√5)/(-1/√5)=2或...