[填空题]
Each string on a violin is tune:xqoq)j5 ky e-.u lh0td to u jq;d93me +i5yz vvu3a frequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ = $\mu_{A}$
$f_{B}$ = $\mu_{A}$
$f_{C}$ = $\mu_{A}$
