Question

Write an explicit formula for the sequence and find the first 5 terms

Answer 1

I'm assuming we're working with geometric sequences.
$a_1 = 100, r = -20$
$T_n = 100(-20)^{n - 1}$
$T_1 = 100, T_2 = -2000, T_3 = 40000, T_4 = -80000, T_5 = 16 000 000$

$a_1 = 10, r = -1$
$T_n = 10(-1)^{n - 1}$
$T_1 = 10, T_2 = -10, T_3 = 10, T_4 = -10, T_5 = 10$