To get the discount rate, isolate $r$
$ \dfrac{\text{FV}}{(1 + r)^t}= \text{PV} $ [multiply by $(1+r)^t$ and divide by PV]
$\dfrac{\text{FV}}{\text{PV}} = (\text{1 + r})^t$ [raise to exponent $1/t$]
$\left(\dfrac{\text{FV}}{\text{PV}}\right)^{1/t} = (\text{1 + r})^{t/t}$ $= 1+r$ [subtract $1$]