Assuming you know the asymptote rules. We want to use the one that states if numerator's degree = 1 + denominators degree, the asymptote is a slant symptote in the form of y = mx + b.
![\lim_{n \to \infty} \frac{f(x)}{x} \ \textgreater \ \lim_{n \to \infty} [tex] \lim_{n \to \infty} ( \frac{x + 9}{x^2} + 2x + 3 - 2x) \ \textgreater \ refine \ \textgreater \ \lim_{n \to \infty} ( \frac{x + 9}{x^2} + 3)](https://tex.z-dn.net/?f=%20%5Clim_%7Bn%20%5Cto%20%5Cinfty%7D%20%20%5Cfrac%7Bf%28x%29%7D%7Bx%7D%20%5C%20%5Ctextgreater%20%5C%20%20%20%5Clim_%7Bn%20%5Cto%20%5Cinfty%7D%20%5Btex%5D%20%5Clim_%7Bn%20%5Cto%20%5Cinfty%7D%20%28%20%5Cfrac%7Bx%20%2B%209%7D%7Bx%5E2%7D%20%2B%202x%20%2B%203%20-%202x%29%20%5C%20%5Ctextgreater%20%5C%20%20refine%20%5C%20%5Ctextgreater%20%5C%20%20%20%5Clim_%7Bn%20%5Cto%20%5Cinfty%7D%20%28%20%5Cfrac%7Bx%20%2B%209%7D%7Bx%5E2%7D%20%20%2B%203%29)
\ \textgreater \ 2 [/tex]
Now write the exception of indeterminate form.

For

we want to divide by the highest denominator power.

Write the exception again.

Apply the infinite property to both!

For 3 apply

Now combine our terms and we get y = 2x + 3