Question

Find the sum of a finite arithmetic sequence from n = 1 to n = 18, using the expression 4n − 10. (1 point) 56 116 504 1,016

Answer 1

684-180=504

Explanation:

Answer 2

`a_n = 4n - 10 \\ a_1 = 4 - 10 = -6 \\ a_2 = 8- 10 = -2 \\ a_3 = 12 - 10 = 2 \\ a_18 = 72 - 10 = 62`

a = -6

d = 4

`a_n = a + (n - 1)d \\ 62 = -6 + (n - 1)4 \\ 68/4 = n - 1 \\ n = 17 + 1 \\ n = 18`

`S_n = n/2 × (a + a_n) \\ S_n = 18/2 × ( -6 + 62) \\ S_n = 9 × 56 = 504`