Based on the simple axiom [math]\pi = \iint_{\sigma_1}^{\sigma_2} \underbrace{\overbrace{2\rho r^{2,\overbrace{1}^{2-1}}_1}^{r=\sigma'''(x)}}_{Note: \rho=\sigma(1)} \partial\rho[/math], how do we get the area of a circle?
valid question