294. $\int_{1}^{e} \frac{3 \ln ^{2} x d x}{x}$.

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294. $\int_{1}^{e} \frac{3 \ln ^{2} x \, dx}{x}$.
Solution. $\int_{1}^{e} \frac{3 \ln ^{2} x d x}{x}=\left|\begin{array}{l}\ln x=t, t_{1}=\ln 1=0, \\ \frac{d x}{x}=d t ; t_{2}=\ln e=1\end{array}\right|=3 \int_{0}^{1} t^{2} d t=\left.t^{3}\right|_{0} ^{1}=1$.