Find the sum of the first 33 terms of the arithmetic sequence whose first term is 3 and whose 33rd term is -253

Answer 1

As you (should) know,

Sn = n/2 (a1 + an)
S33 = 33/2 (a1 + a33)
= 33/2 (3 - 253)
= 33/2 (-250)
= -33*125 = -4125