2x-6y+1=0斜率是1/3所以所求直线斜率是-3y=x³+3x²-5y'=3x²+6x所以斜率k=y'=3x²+6x=-33(x+1)²=0x=-1所以切点横坐标是-1y=-1+3-5=-3切点(-1-3)所以y+3=-3(x+1)即3x+y+6=0...