13x^2-7x+m=0 sina+cosa=7/13 sina*cosa=m/13 (sina+cosa)^2=1+2sina*cosa=1+2m/13=(7/13)^2 m= -60/13tana=-12/5 or tana=-5/12 (1-tana)/cos 2a×（1+tana）=(1-tan^2a)/cos2a=1-tan^4a=20111/20736 or -20111/625...