Here's why:

* The relationship: Wavelength and frequency are inversely proportional. This means that as one increases, the other decreases.

* The equation: This relationship is defined by the following equation:

c = fλ

Where:

* c is the speed of light (a constant)

* f is the frequency

* λ is the wavelength

* Doubling the wavelength: If you double the wavelength (λ), to keep the equation balanced, the frequency (f) must be halved.

Example:

* Imagine a wave with a wavelength of 1 meter and a frequency of 1 Hz.

* If you double the wavelength to 2 meters, the frequency will decrease to 0.5 Hz.