What is the sum of the following expression:
(a+(2n+1)d)2−(a+(2n)d)2+(a+(2n−1)d)2−(a+(2n−2)d)2+⋯+(a+d)2−a2.
Any help would be appreciated
(a + (2n + 1)d)^2 - (a + (2n)d)^2 + ... + (a + d)^2 - a^2 = (a + (2n + 1) d + (a + 2nd + ... + a + d) + a = n(3a + (n + 2)d).
