[tex]\begin{array}{l}\begin{cases} \begin{array}{l}\sin \alpha =\frac{x}{12} \Leftrightarrow x=12\sin \alpha \end{array}\\\cos \alpha =\frac{y}{12} \Leftrightarrow y=12\cos \alpha \end{cases}\\\\\text{Thus,\ the\ area\ is}\\\\A=\frac{xy}{2} =\frac{12\sin \alpha \cdotp 12\cos \alpha }{2}\\\\\Longrightarrow A=72\sin \alpha \cos \alpha \end{array}[/tex]
D
