tan（45+x）=3（tg45+tgx)/(1-tg45tgx)=3(1+tgx)/(1-tgx)=3tgx=1/2sin2x=2tgx/(1+tgx^2)=4/5cos2x=(1-tgx^2)/(1+tgx^2)=3/5sin2x-2cos²x =sin2x-cos2x-1=4/5-3/5-1=-4/5