Find the value of the sum n∑r=1 n∑s=1δrs2r3s where δrs is zero if r≠s & δrs is one if r=s
Given δrs=0ifr≠sδrs=1ifr=s
∴n∑r=1n∑s=1δrs2r3s
=n∑r=12r3r=n∑r=16r=6+62+63+..6n=6(6n−1)5