Hello Tutors, I have a problem with the table below. It is from: The topic is Interference (light, optics). https://studylib.net/doc/25197982/16468-interference-and-diffraction-from-resnik-and-halliday.

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Table 35-1 An Organizing Table for Thin-Film Interference in Air (Fig. 35-17)a Reflection phase shifts 0.5 wavelength O Path length difference 2L Index in which path length difference occurs no In phase : 2L - odd number X 2 Out of phased: 2L = integer X 7