Find a formula for the exponential function passing through the points $(-1,135)$ and $(2,5)$
$$f(x)=$$

Step 1 ：The general form of an exponential function is $f(x)=a{b}^x$. We can use the two given points to form a system of equations and solve for $a$ and $b$.

Step 2 ：From the point $(-1,135)$, we get the equation $135=a{b}^{-1}$ or $135=a/b$.

Step 3 ：From the point $(2,5)$, we get the equation $5=a{b}^2$.

Step 4 ：We can solve this system of equations to find the values of $a$ and $b$.

Step 5 ：The solution to the system of equations gives us three possible solutions for $a$ and $b$. However, since we are dealing with an exponential function, we know that $b$ must be positive. Therefore, we can discard the solutions where $b$ is negative or complex. This leaves us with the solution $(a,b)=(45,1/3)$.

Step 6 ：So, the exponential function that passes through the points $(-1,135)$ and $(2,5)$ is $f(x)=45\ast (1/3{)}^x$.

Step 7 ：$\boxed{{\displaystyle f(x)=45\ast (1/3{)}^x}}$