3次方程 （英文）x^3+p*x^2+q*x+r=0set z=x-k rewrite the function as a cubic equation in z.(后面省略一点)变成关于Z的方程后,让Z的二次项消失,得z^3-a*z+b=0write down a condition on the coefficients that is satisfield if and on

3次方程 （英文）x^3+p*x^2+q*x+r=0set z=x-k rewrite the function as a cubic equation in z.(后面省略一点)变成关于Z的方程后,让Z的二次项消失,得z^3-a*z+b=0write down a condition on the coefficients that is satisfield if and on
3次方程 （英文）
x^3+p*x^2+q*x+r=0
set z=x-k rewrite the function as a cubic equation in z.(后面省略一点)
变成关于Z的方程后,让Z的二次项消失,得
z^3-a*z+b=0
write down a condition on the coefficients that is satisfield if and only if the cubic has two turning points（local max and local min）

3次方程 （英文）x^3+p*x^2+q*x+r=0set z=x-k rewrite the function as a cubic equation in z.(后面省略一点)变成关于Z的方程后,让Z的二次项消失,得z^3-a*z+b=0write down a condition on the coefficients that is satisfield if and on
化成Z的方程后,对Z求一次导,让导数＝0求得系数之间的关系即可.
two turning points,就是指Z的三次方程的一次导数与X轴有且仅有两交点.Z的图形应该仅有两条切线的斜率为0,即拐两弯