Let f be the fundamental frequency of the string. If the string is divided into three segments l1, l2 and l3 such that the fundamental frequencies of each segments be f1, f2 and f3, respectively. Show that
\(\frac { 1 }{ f } =\frac { 1 }{ { f }_{ 1 } } +\frac { 1 }{ { f }_{ 2 } } +\frac { 1 }{ { f }_{ 3 } } \)
