Question

If a1 =5 and an=-2an-1 then find the value of a4

Answer 1

We are given the following recursive formula:

an = -2an-1

We are also given that a1 = 5. Using the recursive formula, we can find the values of a2, a3, and a4 as follows:

a2 = -2a1 = -2(5) = -10

a3 = -2a2 = -2(-10) = 20

a4 = -2a3 = -2(20) = -40

Therefore, the value of a4 is -40.