+39 
i have a test today on these topics and this is the review, these are a few of those questions and i don't know how to do them. pls help me with the explanation
+605 For the first one - $f(n)=2*f(n-1)$, I'll leave you to find the starting condition.
A recursive formula is when you write $f(x)$ in terms of $f(x-1)$. Explicit is when you have some exact equation like $f(x)=3x+4$. Arithmetic is when we add a number to the last number - geometric is when we multiply.
You should be able to do these now.
