  Fix $\left\{a_1, \dots, a_n \right\} \subset \mathbb{N}$, and let $x$ be a
uniformly distributed random variable on $[0,2\pi]$. The probability
$\mathbb{P}(a_1,\ldots,a_n)$ that $\cos(a_1 x), \dots, \cos(a_n x)$ are either
all positive or all negative is non-zero since $\cos(a_i x) \sim 1$ for $x$ in
a neighborhood of $0$. We are interested in how small this probability can be.
Motivated by a problem in spectral theory, Goncalves, Oliveira e Silva, and
Steinerberger proved that $\mathbb{P}(a_1,a_2) \geq 1/3$ with equality if and
only if $\left\{a_1, a_2 \right\} = \gcd(a_1, a_2)\cdot \left\{1, 3\right\}$.
We prove $\mathbb{P}(a_1,a_2,a_3)\geq 1/9$ with equality if and only if
$\left\{a_1, a_2, a_3 \right\} = \gcd(a_1, a_2, a_3)\cdot \left\{1, 3,
9\right\}$. The pattern does not continue, as $\left\{1,3,11,33\right\}$
achieves a smaller value than $\left\{1,3,9,27\right\}$. We conjecture
multiples of $\left\{1,3,11,33\right\}$ to be optimal for $n=4$, discuss
implications for eigenfunctions of Schr\"odinger operators $-\Delta + V$, and
give an interpretation of the problem in terms of the lonely runner problem.
