Solution
= Solution
For $\nu=5$, $B$ is real symmetric. <Sylvester's criterion> says that all <eigenvalues> are positive exactly when its leading principal <matrix minors> are positive. These are $1$, $5-4=1$, and $\det B=1-\mu^2$. Therefore
$$
\boxed{-1<\mu<1.}
$$
At either endpoint one <eigenvalue> is zero, so the strict positivity requirement excludes it.