Final answer:
The function to model the area of the pig pen with 36 feet of fencing as a function of side length x is A(x)=18x-x^2.
Step-by-step explanation:
Pablo wants to build a rectangular pen for the pig he is raising and has 36 feet of fencing. The representative function that can be used to model the area of the rectangular pen as a function of the side length, x, is option (C) A(x)=18x-x^2. Here's why: if x represents one side of the rectangle, the adjacent side would be (36 - 2x) over 2, since there are two sides of length x and two of length (36 - 2x) over 2 to account for in the total fencing length. The area A, therefore, is the product of these sides, which simplifies to A(x)=18x-x^2.