x⁴-3x³-15x²+19x+30=0
x⁴+x³-4x³-4x²-11x²-11x+30x+30=0
x³(x+1)-4x²(x+1)-11x(x+1)+30(x+1)=0
(x+1)(x³-4x²-11x+30)=0
(x+1)(x³-2x²-2x²+4x-15x+30)=0
(x+1)[x²(x-2)-2x(x-2)-15(x-2)]=0
(x+1)(x-2)(x²-2x-15)=0
(x+1)(x-2)(x-5)(x+3)=0
∴x=-3,-1,2,或5