Are There Any 'Horizontal Asymptote' Rule Exceptions?
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An equation I have is $$F(x) = \frac{9x(x-9)}{3x^2-11x-4}.$$

Upon calculating using the rules taught in class,

There is an H.A. at $y = 3$ and a V.A. at $x = -\frac13$ and at $4.$

After graphing, V.A. seems to be correct, but if I plug in $23/11$ as the $x$ value, it still returns $3$.

Are there any exceptions to when to use the rule to find out H.A.?

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2 Answers

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Remember that an horizontal asymptote can cross the curve (there are even examples when this happens infinitely many times). The horizontal asymptote only describes the curve's behaviour for $x\to\pm \infty$.

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$$y=\lim _{ x\rightarrow +\infty }{ \frac { 9x\left( x-9 \right) }{ 3{ x }^{ 2 }-11x-4 } = } \lim _{ x\rightarrow +\infty }{ \frac { { x }^{ 2 }\left( 9-\frac { 81 }{ x } \right) }{ { x }^{ 2 }\left( 3-\frac { 11 }{ x } -\frac { 4 }{ { x }^{ 2 } } \right) } = } 3$$ so $$y=3$$ is your horizontal asymptote

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Chloe Bennett

Chloe Bennett

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Chloe Bennett explores the intersection of pop culture, streaming entertainment, digital trends, and contemporary lifestyle. Her weekly commentary reaches thousands of culture enthusiasts.

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