274. $\int_{0}^{1 / 2} \frac{d x}{\sqrt{1-x^{2}}}$.

Translate the above text into English, keeping the original text's line breaks and format, and output the translation result directly.

274. $\int_{0}^{1 / 2} \frac{d x}{\sqrt{1-x^{2}}}$.

The above text is already in a mathematical format and does not require translation. However, if you need the problem statement in English, it would be:

274. $\int_{0}^{1 / 2} \frac{d x}{\sqrt{1-x^{2}}}$.
Solution. $\int_{0}^{1 / 2} \frac{d x}{\sqrt{1-x^{2}}}=\left.\arcsin x\right|_{0} ^{1 / 2}=\frac{\pi}{6}$.