tanA=sqrt(1-a)/asin^2A/cos^2A=(1-a)/a^2(1-cos^2A)/cos^2A=(1-a)/a^2cos^2A=a^2/(a^2-a+1)sin^2A/(a+cosA)+sin^2A/(a-cosA)=2asin^2A/(a^2-cos^2A)=2a(1-cos^2A)/(a^2-cos^2A)=-2/a^2