Compute the sum (a +(2n+1)d)^2- (a + (2n)d)^2 +(a + (2n-1)d)^2 - (a+(2n-2)d)^2 + ... + (a+d)^2 - a^2
I am confused, how can I figure out the number of terms from here? I know that it decreases by d with each term. But I don't know that number of terms. How does 2n-1 become 0?
