(sin 2a--1)/(1+cos 2a)= -(sin²a+cos²a-2sinacosa)/(1+2cos²a-1)=-(sin²a+cos²a-2sinacosa)/(2cos²a)=-(1/2)[tan²a+1-2tana]=-(1/2)*(3²+1-2*3)=-(1/2)*4=-2