Question

If a1 =9 and an = -2an-1 then find the value of a4

Answer 1

Answer:

Step-by-step explanation:

$a_1=9\\ \\ a_n=-2a_{n-1}\\ \\ a_n=9(-2^{(n-1)})\\ \\ a_4=9(-2^{(4-1)})\\ \\ a_4=9(-2)^3\\ \\ a_4=9(-8)\\ \\ a_4=-72$