Respuesta :
The speed remains the same but the frequency decreases as wavelength increases and vice versa as v=f X wavelength
==> As you started by saying, all EM waves travel at the same speed in vacuum.
==> As the wavelength doubles, the frequency drops by half. Their product is always the speed, which doesn't change.
==> As the wavelength doubles, the frequency drops by half. Their product is always the speed, which doesn't change.