+22 It would be great if someone could help explain this a bit to me, I believe we have to use difference of squares but I dont really know. Thanks!
\(Compute the sum (a +(2n+1)d)^2- (a + (2n)d)^2 +(a + (2n-1)d)^2 - (a+(2n-2)d)^2 + \cdots + (a+d)^2 - a^2.\)
