Question

What is the 20th term of the arithmetic sequence 3, -3, -9, ... ?

Answer 1

a = 3
d = -3 -3 = -6

\[t_n = a + (n-1)d\]

Put n = 20 here,

\[\large t_{20} = 3 + (20-1)(-6)\]

\[\large t_{20} = 3 - 114\]

\[\large t_{20} = -111\]

Answer 2

same thing :D but a bit different