### Functions: Fractional functions

### Asymptotes and hyperbolas

Take a look at the function #f(x)=\tfrac{1}{x}#. In the graph we see that the function consists of two **branches** . This is because #0# is not part of the domain of the function and hence, #f(0)# does not exist. We name a graph consisting of two branches a #\blue{\textbf{hyperbola}}#.

We see that, if #x# becomes really negative or if #x# becomes really positive, the graph approaches the #x#-axis really close. However, the function value never becomes equal to #0#. We call the #x#-axis, the line #y=0#, the #\purple{\textbf{horizontal asymptote}}# of the graph.

We also see that if the #x#-value approaches #0# from the negative side, the function value becomes arbitrarily negative: it decreases without any bound. On the other hand, if the #x#-value approaches #0# from the positive side, #f(x)# becomes arbitrarily positive. We call the #y#-axis, the line #x=0#, the #\green{\textbf{vertical asymptote}}# of the graph.

Asymptote and hyperbola

An **asymptote** is a line which the function approaches closer and closer, but with which the graph never touches or coincides.

A **hyperbola** is a function which has a graph consisting of two separate parts because of its asymptotes. These two separate parts are also called the **branches** of the graph.

The horizontal asymptote is: #y=0#

After all, the vertical asymptote can be found by investigating which values for #x# cannot be entered in the function. In a fractional function, the denominator cannot be equal to #0#. The vertical asymptote is therefore equal to #x=-9#.

The horizontal asymptote can be found by entering very high values for #x# and next investigating what happens with the function. If we enter very high values of #x# then, #x+9# becomes very big. Next #{{1}\over{x+9}}# approaches closer and closer to #0#, but never becomes equal to #0#. The horizontal aysmptote is therefore equal to #y=0#.

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