Explain the world in math

Edited. Inline math eiπ+1=0e^{i\pi} + 1 = 0 and variance σ2=1N∑i=1N(xi−μ)2\sigma^2 = \frac{1}{N}\sum_{i=1}^{N}(x_i - \mu)^2 here.

Mathblock:

ϕ(r)=q4πε0r+−q4πε0r−\phi(\mathbf{r})=\frac{q}{4 \pi \varepsilon_0 r_{+}}-\frac{q}{4 \pi \varepsilon_0 r_{-}}