$\int_{\frac{-\pi}{4}}^{\frac{\pi}{4}} \frac{e^x \cdot x \cdot \sin x}{e^{2 x}-1} \mathrm{~d} x=0\left[\begin{array}{c}a \\ \because \int_{-a}^a f(x) \mathrm{d} x=0 \\ \text { if } f(x) \text { is an odd function }\end{array}\right]$