The negative one power isn't being applied to the frames, we're dealing with frames * inverse seconds
also, fp^-1 makes no sense, fps is shorthand for frames per second, "per" is not a unit unto itself, it's telling us that seconds are inverse (1/s, or s^-1). At no point are we dealing with inverse frames. just like Miles per hour tells us that if you're going 80mph, you are travelling at 80 miles per every 1 hour, 80m/h. So it's modifying the unit that comes after, not before. Per is just a verbal way to say "/", you could say "over", or any other equivalent statement as well.
Frames per second = number of frames in a second
this is represented as (X Frames / second)
This can also be represented as:
>Frame Hertz
>>fHz
since Hz is itself shorthand for inverse seconds (1/s, s^-1)
>X Frames * Hz
>>= XFrames *1/s
>>> =X frames/s
>>>>= frames * s^-1
Now, if we have inverse Hz (Hz^-1) (since that's what I was addressing)
then it's 1/(1/s)
OR
1/(s^-1)
therefore
X Frames * Hz^-1
> =XFrames *(1/Hz)
>> =X Frames * (1/(1/s))
>>> = Xframes * s
>>>> fs