Here's why:

* The relationship: The speed of a wave is determined by the product of its frequency and wavelength. This relationship is represented by the equation:

* Speed (v) = Frequency (f) x Wavelength (λ)

* Constant speed: For a given medium, the speed of a wave remains constant.

* The consequence: If you double the frequency (f), to keep the speed (v) constant, the wavelength (λ) must be halved.

In other words, frequency and wavelength are inversely proportional.