y=x^3的导数为y=3x^2,直线与其切点为（m,m^3）则直线过（m,m^3）,(1,0)求得直线为y=0或者y=27/4*(x-1)若y=0.则y=ax^2+15/4x-9顶点在x轴得a=-25/64若y=27/4*(x-1),斜率为27/4y=ax^2+15/4x-9的导数为y=2ax+15/4,直线与...