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 \(f(x) = ab^x\). 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 \(135 = ab^{-1}\) or \(135 = a/b\).

Step 3 ：From the point \((2, 5)\), we get the equation \(5 = ab^2\).

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 \(f(x) = 45*(1/3)^x\).

Step 7 ：\(\boxed{f(x) = 45*(1/3)^x}\)