Natural number

${\displaystyle \sum _{i=1}^n{i}^3={\left(\frac{n(n+1)}{2}\right)}^2}$

${\displaystyle {(1-l)}^n={(1-l)}^{\frac{ln}{l}}=\underset{l\to 0}{lim}{e}^{-ln}}$
${\displaystyle Q_{ch}={\int }_{V_1}^{V_2}i\left(t\right)dt}$
where