The frequency in the formula is where the speakers response is 3db down.
A single capacitor will only give you a 6 db per octave roll off so the speaker will have appreciable output at least 2 octaves lower than that. If you crossover at 200 then the speaker will only be 6 db down at 100 and 12 db down at 50.
I would guess that the speaker itself already way down at 200 hz so you would be adding the crossover to the response of the speaker. You might be OK without any crossover depending on where you bring the woofer in.