I have several independent variables & one dependent variable for a regression model.
One of these IVs have a much better curve fit (with the DV) as quadratic regression.
I was thinking about transforming the IV (by squaring it) and then adding both the IV and its squared value in the multiple linear regression model.
However, I've heard that if I do that, I can only keep either one or the other (i.e. either the IV or its squared values) in the regression model because they're co-dependent.
What would be the correct way to go about this? Can I add quadratic regression to a multiple linear model at all?