函数 $f(t)=\sin^2 t$ 的傅氏变换 $\mathcal{F}[f(t)]$ 为().

• A. $-\frac{\pi}{2}[\delta(\omega-2)-2\delta(\omega)+\delta(\omega+2)]$;
• B. $-\frac{\pi}{2}i[\delta(\omega-2)-2\delta(\omega)+\delta(\omega+2)]+$
• C. $-\frac{\pi}{2}[\delta(\omega-2)+2\delta(\omega)+\delta(\omega+2)]$;
• D. $-\frac{\pi}{2}i[\delta(\omega-2)+2\delta(\omega)+\delta(\omega+2)].+$

已知$f(x)=\int_{0}^{x}e^{\sqrt{t}}\,dt$，求$f(1)=$(）. A. 0B. 0C. 1D. $e$E. $e^{-1}$

证明：点集 $F$ 为闭集的充要条件是 $\overline{F} = F$. 证明：点集 $F$ 为闭集的充要条件是 $\overline{F} = F$.

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Q235BF钢中的F表示沸腾钢。. Q235BF钢中的F表示沸腾钢。.