Answer: To substitute e^(-7/9) for the variable x in a function, you simply replace every instance of x with e^(-7/9) in the function.
Let's say we have a function f(x) = 2x + 5. To substitute e^(-7/9) for x in this function, we replace x with e^(-7/9):
f(e^(-7/9)) = 2(e^(-7/9)) + 5.
Simplifying this expression, we multiply 2 by e^(-7/9), which gives us:
f(e^(-7/9)) = 2e^(-7/9) + 5.
So, substituting e^(-7/9) for x in the function f(x) = 2x + 5 results in f(e^(-7/9)) = 2e^(-7/9) + 5.
Remember, this process of substitution is applicable to any function. You can substitute a specific value or expression for the variable in the function to evaluate it at that point.