Natural number

`sum_(i=1)^n i^3=((n(n+1))/2)^2`

`(1-l)^n=(1-l)^((ln)/l)=lim_(l->0)e^(-ln)`
`Q_(ch)=int_(V_1)^(V_2)i(t)dt`
where `(V_1)<(V_2)`