A string vibrates at its third-harmonic frequency. The amplitude at a point 30 cm from one end is half the maximum amplitude. How long is the string? i figured since the amplitude at point 30 cm is half the max amplitude, the amplitude must be at 60 cm. The third harmonic frequency means that there are 4 nodes and 3 antinodes. i keep getting 1.2 for the length of one but since there are 3, i multiplied 1.2 x 3 and got 3.6m but i don't think that answer can be right. thanks for the help!