Here's why:

* The relationship between frequency, wavelength, and the speed of light: The speed of light (c) is a constant. It's related to frequency (f) and wavelength (λ) by the equation:

* c = fλ

* Constant frequency means constant wavelength: If the frequency (f) is constant, and the speed of light (c) is also constant, then the wavelength (λ) must remain constant as well.

In simpler terms: Imagine you're sending waves in a pool. The frequency of the waves is how many waves pass a certain point per second. If you keep that frequency the same, the distance between each wave (the wavelength) will also stay the same, no matter how fast the waves are traveling.