Compute the sum
\((a +(2n+1)d)^2- (a + (2n)d)^2 +(a + (2n-1)d)^2 - (a+(2n-2)d)^2 + \cdots + (a+d)^2 - a^2.\)
See answer #2 here: https://web2.0calc.com/questions/please-help-question-not-answered#r2
thx so much
