Question

Find an equation for the nth term of the arithmetic sequence.

a19 = -92, a20 = 6

Choices:
an = -1856 + 98(n - 1)
an = -1856 - 98(n - 1)
an = -1856 - 98(n + 1)
an = -1856 + 98(n + 1)

Answer 1

a19 = -92
a20 = 6
common difference = d = a20 - a19
d = 6 - (-92)
d = 6 + 92
d = 98
formula for nth term
an = a1 + (n-1)d
put n = 20
a20 = a1 + (20-1)d
6 = a1 + 19(98)
6 = a1 + 1862
6 - 1862 = a1
-1856 = a1
a1 = -1856
now nth term:
an = a1 + (n-1)d
an = -1856 + (n-1)98
an = -1856 + 98(n-1)