能看明白
分解因式：(x-1)·x³+7(x-1)·x²+13(x-1)·x+4(x-1)=0∴(x-1)·(x³+7x²+13x+4)=0∴(x-1)·[(x+4)·x²+(x+4)·3x+(x+4)]=0∴(x-1)·(x+4)·(x²+3x+1)=0∴方程有四个实根x=1，x=-4，x=(-3+√5)/2，x=(-3-√5)/2
