Set up two limits of the function
[tex]\lim_{x \to \infty} f(x)= \lim_{x \to \infty} 9x=\infty\\ \lim_{x \to -\infty} f(x)= \lim_{x \to -\infty} 9x=-\infty[/tex]
This answer makes sense because f(x) has a positive correlation with x. This means as x increases so does f(x). If we make x infinitely negative, f(x) will also get infinitely negative. Same logic for driving x to positive infinity.
Also, just look at the graph of f(x)=9x. We can see that is a continuous function that grows without bounds. So, it makes sense that if x goes to infinity so will the function and if x goes to -infinity the function will go to -infinity.
