\widehat{ac}The \widehat{ac} command in LaTeX is used to place a hat accent over the specified characters, in this case, 'ac'. This is often used in mathematical notation to denote estimators, transforms, or to highlight specific variables or vectors.
Sample mean notation in statistics
\widehat{ac} = \frac{1}{n}\sum_{i=1}^{n}x_iConvergence of an estimator to a parameter
\widehat{ac} \to \thetaFourier transform of a function ac
\widehat{ac} = \mathcal{F}(ac)