find the sum of the arithmetic series

Question

7+4+1+....+(32).

Answer 1

I assume the (32) means there are 32 terms. If so, then since
a = 7
d = -3
S32 = 32/2 (2*7 + 31(-3)) = -1264
or,
a_32 = 10-32*3 = -86
S32 = 32/2 (7-86) = -1264