GMAT Problem Solving Question 12: Function properties

 
The following GMAT Problem Solving question tests your understanding of properties of functions.

Question 12:

Which of the following functions $f$ satisfies the condition $f(x+y) = f(x) \cdot f(y)$ for all non-zero values of $x$ and $y$?

1. $\quad f(x)=\dfrac{1}{x}$
2. $\quad f(x)=3^{-2x}$
3. $\quad f(x)=-x$
4. $\quad f(x)=\sqrt{x}$
5. $\quad f(x)=x^2-x$