Решебник по геометрии 9 класс Мерзляк Задание 239

\[\textbf{а)}\ S = a^{2} \bullet \frac{1}{2} = \frac{a^{2}}{2};\]

\[\textbf{б)}\ S = a^{2} - S_{a} = a^{2} - \pi \bullet \left( \frac{a}{2} \right)^{2} =\]

\[= a^{2} - \pi \bullet \frac{a^{2}}{4} = a^{2}\left( 1 - \frac{\pi}{4} \right);\]

\[\textbf{в)}\ S = \frac{1}{2}S_{a} - S_{\frac{a}{2}} =\]

\[= \frac{1}{2}\pi \bullet \left( \frac{a}{2} \right)^{2} - \pi \bullet \left( \frac{a}{4} \right)^{2} =\]

\[= \frac{1}{2}\pi \bullet \frac{a^{2}}{4} - \frac{\pi a^{2}}{16} =\]

\[= \pi a^{2}\left( \frac{1}{8} - \frac{1}{16} \right) = \frac{\pi a^{2}}{16}.\]