$\mathop {Lim}\limits_{n \to \infty } $$\frac{\pi }{{2\,n}}\,\,\left( {1\,\, + \,\,\cos \,\frac{\pi }{{2\,n}}\,\, + \,\,\cos \,\frac{{2\,\pi }}{{2\,n}}\,\, + \,\,.....\,\, + \,\,\cos \,\frac{{(n\, - \,1)\,\pi }}{{2\,n}}} \right)$ equal to
→Diffrential coefficient of ${\left( {{x^{\frac{{\ell \, + \,m}}{{m\, - \,n}}}}} \right)^{\frac{1}{{n\, - \,\ell }}}}\,\,\,\,.\,\,\,\,{\left( {{x^{\frac{{\,m + \,n}}{{n\, - \,\ell }}}}} \right)^{\frac{1}{{\,\ell \, - \,m}}}}\,\,\,.\,\,\,{\left( {{x^{\,\frac{{n\, + \,\ell \,}}{{\ell \,\, - \,\,m}}}}} \right)^{\frac{1}{{m\, - \,n\,}}}}\,$ w.r.t. $x$ is
→