Determine the Integral
∫ − T / 2 T / 2 e j 2 π ( n − m ) t / T d x = { T for n = m 0 else {\displaystyle \int _{-T/2}^{T/2}e^{j2\pi (n-m)t/T}\,dx=\left\{{\begin{array}{rcl}T&{\mbox{for}}&n=m\\0&{\mbox{else}}\end{array}}\right.}
