sina+cosa=根号3／3(sina+cosa)^2=(根号3／3)^2,(sina)^2+(cosa)^2+2sinacosa=1/3,1+2sinacosa=1/3,2sinacosa=-2/3,sinacosa=-1/3tana+cota=sina/cosa+cosa/sina=[(sina)^2+(cosa)^2]/(sinacosa)=1/(sinacosa)=1/(-1/3)=-3