显然X=10是方程的解,于是对左式提取因式(x-10)得：
X^3-60X^2+900X-4000=(X-10)(X^2-50X+400)=(X-10)(X-10)(X-40)
所以：(X-10)2(X-40)=0
X1=X2=10,X3=40