Science:Math Exam Resources/Courses/MATH110/April 2017/Question 04 (a) (iii)

MATH110 April 2017

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Question 04 (a) (iii)
Consider the function $f(x)={\frac {x^{2}-3x+2}{x^{3}-2x^{2}}}$ (iii) Find all vertical asymptotes of $f$, if they exist. Justify your answer

Make sure you understand the problem fully: What is the question asking you to do? Are there specific conditions or constraints that you should take note of? How will you know if your answer is correct from your work only? Can you rephrase the question in your own words in a way that makes sense to you?

If you are stuck, check the hint below. Consider it for a while. Does it give you a new idea on how to approach the problem? If so, try it!

Hint
Recall that the vertical line $x=a$ is a vertical asymptote of the graph of $f(x)$ if either or both of the one-sided limits, as $x\to a^{-}$ or $x\to a^{+}$ of $f$ is infinite. In order to determine the limits, use the factorization of the numerator and the denominator of $f(x)$ as in the previous parts of the question.

Checking a solution serves two purposes: helping you if, after having used the hint, you still are stuck on the problem; or if you have solved the problem and would like to check your work. If you are stuck on a problem: Read the solution slowly and as soon as you feel you could finish the problem on your own, hide it and work on the problem. Come back later to the solution if you are stuck or if you want to check your work. If you want to check your work: Don't only focus on the answer, problems are mostly marked for the work you do, make sure you understand all the steps that were required to complete the problem and see if you made mistakes or forgot some aspects. Your goal is to check that your mental process was correct, not only the result.

Solution

Found a typo? Is this solution unclear? Let us know here. Please rate my easiness! It's quick and helps everyone guide their studies. The vertical asymptotes occur where the function becomes infinite. For a fraction to be infinite, either the denominator is zero with a non-zero numerator, or the numerator is infinite with a finite denominator. The numerator is a polynomial so it is defined for all real numbers and is never infinite. The denominator of $f(x)$ is $x^{3}-2x^{2}=(x-2)x^{2}$ so it is zero when $x=2$ and $x=0$. So the only possibilities of a vertical asymptote are when $x=2$ and $x=0$. By part (a) - (ii), $\lim _{x\to 2}f(x)={\frac {1}{4}}$, so $x=2$ is not a vertical asymptote. On the other hand, $\lim _{x\to 0}x^{2}-3x+2=2$, so $\lim _{x\to 0}f(x)=-\infty$. Thus, there is exactly one vertical asymptote of $f(x)$, at $\color {blue}x=0.$