Approximate rate of change from graphs and tables of values - AP Calculus AB

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Question

Which of the following functions contains a removeable discontinuity?

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Answer

A removeable discontinuity occurs whenever there is a hole in a graph that could be fixed (or "removed") by filling in a single point. Put another way, if there is a removeable discontinuity at , then the limit as approaches exists, but the value of does not.

For example, the function f(x)=\frac{1+x^3}{1+x} contains a removeable discontinuity at . Notice that we could simplify as follows:

f(x)=\frac{1+x^3}{1+x}=\frac{(1+x)(x^2-x+1)}{1+x}=x^{2}-x+1, where x\neq -1.

Thus, we could say that \lim_{x\rightarrow -1}\frac{1+x^3}{1+x}=\lim_{x\rightarrow -1}x^2-x+1=(-1)^2-(-1)+1=3.

As we can see, the limit of exists at , even though is undefined.

What this means is that will look just like the parabola with the equation x^{2}-x+1 EXCEPT when, where there will be a hole in the graph. However, if we were to just define , then we could essentially "remove" this discontinuity. Therefore, we can say that there is a removeable discontinuty at .

The functions

, and

have discontinuities, but these discontinuities occur as vertical asymptotes, not holes, and thus are not considered removeable.

The functions

and f(x)=\frac{x+1}{1+x^{2}} are continuous over all the real values of ; they have no discontinuities of any kind.

The answer is

.

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