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## Homework Statement

A bat flies toward a wall, emitting a steady sound with a frequency of 25.0 kHz. This bat hears its own sound plus the sound reflected by the wall.

How fast should the bat fly, v_b, to hear a beat frequency of 220 Hz?

Take the speed of sound to be 344 m/s.

## Homework Equations

f_beat = f_a - f_b

## The Attempt at a Solution

I let the speed of sound be v and let the emitted frequency be f_e and got an expression for the beat frequency:

f_beat = ((v+v_b)/(v-v_b)-1)f_e

Didn't get the right answer... Doing it another way I got

f_beat = (v^2/(v-v_b)^2 - 1)f_e