Select the appropriate Doppler equation when source is approaching the stationary observer where fo is the observed frequency, fs is frequency of source, v is the speed of sound, vs is the speed of source relative to observer?

fo = v-vs/v fs

fo = v-vs/v+vs fs

fo = v/v-vs fs

fo = v/v+vs fs

The appropriate Doppler equation when the source is approaching the stationary observer is 𝑓𝑜 = 𝑣/𝑣 − 𝑣𝑠 𝑓𝑠.

This equation accounts for the increased frequency observed when the source moves toward the observer, as the sound waves are compressed.