由x+2y+m=0得x=-2y-m ①代入3x^2+4y^2=24得16y^2+12my+3m^2-24=0 ②设弦的两个端点坐标为(x1,y1),(x2,y2),弦中点(a,b)则y1,y2是方程的两根由韦达定理得y1+y2=-12m/16=-3m/4所以b=(y1+y2)/2=-3m/8a=[(-2y1-m)+(-2y2-m...