Math 22 Asymptotes

Vertical Asymptotes and Infinite Limits

 If $f(x)$ approaches infinity (or negative infinity) as $x$ approaches $c$ 
 from the right or from the left, then the line $x=c$ is a vertical asmptote of the graph of $f$

Example: Find the a vertical Asymptotes as below:

1) $f(x)={\frac {x+3}{x^{2}-4}}$

Solution:
Notice $f(x){\frac {x+3}{x^{2}-4}}={\frac {x+3}{(x-2)(x+2)}}$
Let the denominator equals to zero, ie: $(x-2)(x+2)=0$, hence $x=-2$ or $x=2$
Therefore, $f(x)$ has vertical asymptotes at $x=2$ and $x=-2$

2) $f(x)={\frac {x^{2}-x-6}{x^{2}-9}}$

Solution:
Notice $f(x){\frac {x^{2}-x-6}{x^{2}-9}}={\frac {(x-3)(x+2)}{(x-3)(x+3)}}={\frac {x+2}{x+3}}$
Let the denominator equals to zero, ie: $(x+3)=0$, hence $x=-3$
Therefore, $f(x)$ has vertical asymptote at $x=-2$

Definition of Horizontal Asymptote

 If $f$ is a function and $L_{1}$ and $L_{2}$ are real numbers, then the statements
 Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \lim_{x\to\infty} f(x)=L_1}
 and Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \lim_{x\to -\infty} f(x)=L_2}

 denote limits at infinity. The line $y=L_{1}$ and Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle y=L_2}
 are horizontal asymptotes 
 of the graph of Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle f}

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