add new variable Circumference^2, add it to the model from e) and run it in Stata. (Circumference^2 indicates how this variable is calculated, but Stata does not accept this as a variable name, so choose a slightly different name, e.g. 'CircumferenceSqr'.) Then add another new variable Height*Circumference^2 to the model and run it. Copy only the Stata output from the largest model to Word. Compared to the model in e), we see that R-squared has improved. On the other hand, none of the slope coefficients is significant anymore.How is this possible? Explain!

So, how is it possible that when I add more variables to the model, R-squared improves but all the p-values of the slope coefficients become bigger (>5%) so that these are not significant anymore?