What are the three longest wavelengths for standing waves on a 280-cm-long string that is fixed at both ends? enter your answers numerically separated by commas?

Three longest wavelengths will correspond to the three modes of vibration that has the least amount of nodes.  For a standing wave on a string fixed on both ends we have the following formula:

Where L is the length of a string and n is the number of nodes of the standing wave.
From this formula, we see that the more nodes you have the lower your wavelength is.
We need to calculate wavelengths for n=1, n=2, and n=3.

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