We know that the general form of the exponential equation is
. We also know that when a>0 and 0<b<1, then this exponential equation will represent an exponential decay.
Now, the expression given to us is

As we can see from this equation, a=5.8>0, and
, thus, 0<b<1, since,
and thus, as per the general form, the given equation
represents exponential decay.
For a better understanding of the explanation provided here, the graph of
has been attached. As can be seen from that graph it indeed is an exponential decay.