0[（sina）^2+sin2a]/[（cosa）^2+cos2a]=[16/25+2*(4/5)*(3/5)]/[(9/25+2*(3/5)^2-1]=(8/5)/(2/25)=20.tana=sina/cosa=4/3.tan(a-5π/4)=(tana-tan5π/4)/(1+tana*tan5π/4)=(4/3-1)/(1+4/3)=1/7.
