Answer
$\displaystyle \lim_{t\rightarrow\infty}I(t)=\infty.$
The index is expected to rise indefinitely in the long run.
Work Step by Step
$t$ is "approaching $+\infty$" means that $t$ is assuming positive values of greater and greater magnitude.
Observing the graph, we see:
As $t$ assumes positive values of greater and greater magnitude, the function value rises without bound.
So, we write
$\displaystyle \lim_{t\rightarrow\infty}I(t)=\infty.$
The index is expected to rise indefinitely in the long run.
