Polynomial Regression多项式回归

一言以蔽之：xi可以是x的n次方

We can combine multiple features into one. For example, we can combine x1 and x2 into a new feature x3 by takingx1⋅x2.

We can change the behavior or curve（弧度）of our hypothesis function by making it a quadratic（平方）, cubic or square root function (or any other form)

特别注意：平方、立方、开方后不要忘记对特征进行放缩