Givens
Sequence 2, - 4, 8, -16, 32 ....
First term = a = 2
Problem
Find the nth term
tn = (-1 )^(n -1) * (a)^n answer or
tn = (-1)^(n - 1) * 2^n
where a is defined as the first term (it usually is given that designation).
Try a few to make sure the formula is correct
n = 1
t1 = (-1)^(1 - 1) * 2^1
t1 = (-1)^0 * 2
t1 = 1 * 2 = 2
n =2
t2 = (-1)^(2 - 1) * 2^2 = (-1)^1 * 4 = -4
