当a=3且曲线y=f(x)过原点(0,0)f(x)=x^3+bx^2+cx+d,d=0∴f(x)=x^3+bx^2+cxf(x)-9x= 0x^3+bx^2+(c-9)x=0x=1或4∴1+b+(c-9)=064+16b+4(c-9)=0b=-11c=19∴f(x)=x^3-11x^2+19x