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**[SOLVED] Standing Sound Waves**

What are the three longest wavelengths for standing sound waves in a 121 cm long tube that is (a) open at both ends and (b) open at one end, closed at the other?

the wavelength equation that i used for open-open was [tex]\lambda[/tex]= 2L/m; where m is the number of modes (m=1,2,3,4.....)

and then for open-closed [tex]\lambda[/tex]= 4L/m; where m is the number of modes (m=1,3,5,7......)

so i have the length, but the one question that i have about this problem is could i start with the lowest number of modes, but if that is true then why ask for the three longest wavelength, so i am kind of lost if anyone could give me a clue on what to do

thanks in advance