Question

What is the 20th term of the arithmetic sequence 2, -4, -10, ?



-130

-124

-118

-112

Answer 1

\[a_n = a+ (n-1)d\]
a_n
is the n'th term


d-->common difference
a-->first term

Answer 2

a[n] = a[1] + (n-1)*d

a[n] = 2 + (n-1)*(-6)

a[n] = 2 -6n + 6

a[n] = -6n + 8

a[20] = -6(20) + 8

a[20] = -112


So the 20th term is -112

Answer 3

So in your problem, n=20,you know, a, d . Find a_n