sina=cos^2a-sin^2asina=1-sin^2a-sin^2a2sin^2a-sina-1=0(2sina+1)(sina-1)=0sina=-1/2,或sina=1当sina=-1/2时：cosa=±根号(1-sin^2a)=±根号3/2tana=-根号3/3,或根号3/3当当sina=1时：cosa=±根号(1-sin^2a)=0tan...