(n-1)²+n²+(n+1)²=3n²+2*1²(n-2)²+(n-1)²+n²+(n+1)²+(n+2)²=5n²+2*2²+2*1²=5n²+2*(2²+1²)51*51+52*52+53*53+.+99*99=(75-24)...