$3$\displaystyle{\displaystyle{ \int { \cos }^{2}xdx }=\displaystyle{ \int \frac{\hspace{2} 1+\cos 2x \hspace{2}}{\hspace{2}2\hspace{2}}dx }}$

　 $3$\displaystyle{ { \cos }^{2}x=\frac{\hspace{2} 1+\cos 2x \hspace{2}}{\hspace{2}2\hspace{2}} }$

より

$3$\displaystyle{\displaystyle{ \int { \cos }^{2}xdx }=\displaystyle{ \int \frac{\hspace{2} 1+\cos 2x \hspace{2}}{\hspace{2}2\hspace{2}}dx }}$