**Find the derivative of the function using the definition of derivative.
f(x) = rx + n**

**a)State the domain of the function. (Enter your answer using interval notation.)**

**Answer:**

f’(x)= r [assuming x is to the power of 1 and n is your constant]

x= (-∞,∞ ) ,because f(x) is linear function and is therefore defined for all real numbers.