The answer is b.
[tex]y=0.5(0.87)^{x}[/tex]
This is true because this exponential function is given by this form:
[tex]f(x)=ka^{x}[/tex]
where [tex]k\ \textgreater \ 0[/tex] and [tex]0\ \textless \ a\ \textless \ 1[/tex]. So given that a = 0.87, that is, a number less than 1, then the equation will represent an exponential decay
