Question

If f(1) = 160 and f(n + 1) = –2f(n), what is f(4)?

Answer 1

`f(1)=160\\f(n+1)=-2f(n)\\\\f(2)=-2\cdot 160=-320\\f(3)=-2\cdot(-320)=640\\f(4)=-2\cdot 640=-1280`

Answer 2

-1280

Explanation:

There are 2 ways you could do this. You could just do the question until you come to the end of f(4). That is likely the simplest way to do it.

f(1) = 160

f(2) = - 2 * f(1)

f(2) = -2*160

f(2) = -320

f(3) = -2 * f(2)

f(3) = -2 * - 320

f(3) = 640

f(4) = - 2 * f(3)

f(4) = - 2 * 640

f(4) = - 1280

I don't know that you could do this explicitly with any real confidence.