Step-by-step explanation:
We know that the number of complete waves formed in 1 sec time is frequency and the distance between two consecutive crests or troughs is wavelength. And we have the formula that
Velocity = wavelength * frequency
or, frequency = velocity / wavelength
Here we can see frequency is directly proportional to velocity and indirectly proportional to wavelength.
So as the wavelength increases frequency decreases and as the wavelength decreases frequency increases.
Hope you understood