1. The problem statement, all variables and given/known data Three radio-equipped plumbing vans are broadcasting on the same frequency f_0. Van 1 is moving north of van2 with a speed of v, van 2 is fixed, and van 3 is moving west of van 2 with a speed of v. What change in frequency (f-f_0) does van 3 hear from van 1? 2. Relevant equations I'm not really sure what equation to use because the doppler shift function doesn't work here.\ 3. The attempt at a solution I'm not really sure where to start from thise. Thanks in advance for all of your help, guys.