$$\frac{\partial \mathcal{L}}{\partial \eta_1}= -\sum_{i=1}^{n}\frac{\frac{\eta_1}{c}-\cos(y_i-\beta_i X_i)}{c-\eta_1\cos(y_i-\beta_i X_i)-\eta_2\sin(y_i-\beta_i X_i)} $$
大きな分母と分子が必要です。
答え1
\dfrac ( displaystyle
fraction) コマンドを から、amsmath
または \mfrac
( medium-sized
fraction, ca 80% of displaystyle) (からnccmath
) から使用できます。
\documentclass{article}
\usepackage[utf8]{inputenc}}
\usepackage{mathtools, nccmath}
\newcommand*{\e}{\mathrm{e}}
\begin{document}
\[ \frac{\partial \mathcal{L}}{\partial \eta_1}= -\sum_{i=1}^{n}\frac{\dfrac{\eta_1}{c}-\cos(y_i-\beta_i X_i)}{c-\eta_1\cos(y_i-\beta_i X_i)-\eta_2\sin(y_i-\beta_i X_i)} \]%
\[ \frac{\partial \mathcal{L}}{\partial \eta_1}= -\sum_{i=1}^{n}\frac{\mfrac{\eta_1}{c}-\cos(y_i-\beta_i X_i)}{c-\eta_1\cos(y_i-\beta_i X_i)-\eta_2\sin(y_i-\beta_i X_i)} \]%
\[ \frac{\partial \mathcal{L}}{\partial \eta_1}= -\sum_{i=1}^{n}\frac{\frac{\eta_1}{c}-\cos(y_i-\beta_i X_i)}{c-\eta_1\cos(y_i-\beta_i X_i)-\eta_2\sin(y_i-\beta_i X_i)} \]%
\end{document}