# Polynomial regression - Week 2: Regression with multiple input variables |

Polynomial Regression - I have a doubt with regards to the following equation
Fw,b(x)=w_1x +w_2x^2+b. Why does the value of price w.r.t size decrease in the case of a quadratic equation but increase in the case of a cubic equation? The intuition isn’t clear to me.

Just wanted to explain the way I understand this before the mentors come.
It depends on the region of the curve you look at. For a quadratic equation, you will definitely have two regions , one where the independent and dependent variable change in the same direction and the other where they change in opposite directions. For a cubic equation or curve, it depends but there are three regions with one maximum and one minimum.
So, if you look at it this way, the way the variables change will depend on your position on the curve.

The weight for each feature can be either positive or negative.

Welcome! If you still have follow-up, please be more specific so that we can see what you were seeing. We know it is course 1 week 2, but video’s name & time mark, or lab’s name will be helpful.

Cheers,
Raymond