Looking at the two graphs, we can see that the end behavior is different from what weβve seen before: it has a horizontal asymptote on one side, while the other blows up to \(\infty\text{.}\)
Fact12.2.3.Finding End Behavior of an Exponential Function.
To find the end behavior of an exponential function, we first need to figure out whether it represents growth or decay. After that, we can use the shape of the graph to determine the end behavior.
Suppose we want to find the end behavior of \(f(x)=7(1.56)^x\text{.}\) Since \(b=1.56\gt 1\text{,}\) we can see that this is exponential growth. Based on the shape of the exponential growth graph, we have the following end behavior:
As \(x\rightarrow -\infty\text{,}\)\(y\rightarrow 0\text{.}\)
Since \(b=0.01\lt 1\text{,}\) we can see that this is exponential decay. Based on the shape of the exponential decay graph, we have the following end behavior:
As \(x\rightarrow -\infty\text{,}\)\(y\rightarrow \infty\text{.}\)
Suppose we want to find the end behavior of \(f(x)=7(1.56)^{x+3}-2\text{.}\) Since \(b=1.56\gt 1\text{,}\) we can see that this is exponential growth. So, we know what the shape of the graph looks like, but notice that we have some transformations here. The \(+3\) is a horizontal shift, which wonβt affect our end behavior, so we can ignore that. However, the \(-2\) shifts the whole graph down. That wonβt affect the side that goes to \(\infty\) (since \(\infty-2\) is still \(\infty\)), but it will move our horizontal asympote down 2. So, we have the following end behavior:
As \(x\rightarrow -\infty\text{,}\)\(y\rightarrow -2\text{.}\)
Since \(b=0.01\lt 1\text{,}\) we can see that this is exponential decay. So, we know what the shape of the graph looks like, but notice that we have some transformations here. The \(-4\) is a horizontal shift, which wonβt affect our end behavior, so we can ignore that. However, the \(+9\) shifts the whole graph up. That wonβt affect the side that goes to \(\infty\) (since \(\infty+9\) is still \(\infty\)), but it will move our horizontal asympote up 9. So, we have the following end behavior:
As \(x\rightarrow -\infty\text{,}\)\(y\rightarrow \infty\text{.}\)