noise cancellation - newbie question

Is it possible to make a pure sine wave of say 500Hz and make it silent, so it can’t be heard when played as a wav file ?
I want a computer to receive the sound wave information and process it.

I realise I can do it with high or low frequencies beyond human hearing, but in this instance I want to do it with a 500Hz sound wave.

I was wondering if noise cancellation techniques could be used ? In which case is it possible for Audactity to create this?

You’ve not really explained how/why you want this, so this may not be quite the right answer for what you want, but give it a try anyway to see what happens:
(instructions assume that you are using the current 1.3.14 version of Audacity)

  1. Generate menu > Generate a 500 Hz sine tone
  2. Select the track and duplicate it (Edit menu)
  3. Select the duplicate track and apply the “Invert” effect.
  4. Solo one track and play it
  5. Solo (only) the other track and play it
  6. Un-solo both tracks and play them.

Playing the inverse of any audio track through the same loudspeaker will result in silence.