Find the indicated nth partial sum of the arithmetic sequence. -2.1, 2.5, 7.1, 11.7, ...., n=90
A)-7996.5
B)18,241
C)18,648
D)18,227
E)18,234

Question

Quizplus · Accepted Answer

The nth partial sum of an arithmetic sequence can be found using the formula S_n = n/2 * (a_1 + a_n). Here, a_1 = -2.1, the common difference d = 4.6, and n = 90. First, find a_n using a_n = a_1 + (n-1)d = -2.1 + 89*4.6 = 405.3. Then, S_90 = 90/2 * (-2.1 + 405.3) = 18,234.

Find the Indicated Nth Partial Sum of the Arithmetic Sequence