= Uncertainty in a cosine of a measured angle
{title2=$\sigma_S^2=\cos^2(q\theta)\sigma_A^2+[qA\sin(q\theta)]^2\sigma_\theta^2$}
For $S=A\cos(q\theta)$ with <independent> <standard uncertainties>, linear propagation gives $\sigma_S^2=\cos^2(q\theta)\sigma_A^2+[qA\sin(q\theta)]^2\sigma_\theta^2$. Angular uncertainty must be in radians when using this derivative. <Covariance> adds cross terms for correlated inputs. Strict error bounds instead add absolute first-order contributions; they do not justify Gaussian significance tests.
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