Circles

1103077210

Level: 
B
The picture shows a roundabout with the radius of \( 6\,\mathrm{m} \). Inside the roundabout there is a flower bed, which has the shape of an equilateral triangle inscribed in it. The remaining part inside the roundabout is the lawn. Calculate the area of the lawn.
\( 66.33\,\mathrm{cm}^2 \)
\( 46.77\,\mathrm{cm}^2 \)
\( 113.10\,\mathrm{cm}^2 \)
\( 24.66\,\mathrm{cm}^2 \)

2000005904

Level: 
B
Find the magnitude of the angle that the diagonals \(DB\) and \(CG\) make in the regular heptagon \(ABCDEFG\). (See the picture.)
\( 180^{\circ}-\left(\frac{360^{\circ}}{14} +3\cdot\frac{360^{\circ}}{14}\right)\)
\( 180^{\circ}-\left(\frac{360^{\circ}}{7} +3\cdot\frac{360^{\circ}}{7}\right)\)
\( 180^{\circ}-\frac{360^{\circ}}{14} +3\cdot\frac{360^{\circ}}{14}\)
\( 180^{\circ}-\left(\frac{360^{\circ}}{14} +4\cdot\frac{360^{\circ}}{14}\right)\)

2000005909

Level: 
B
The regular octagon \(ABCDEFGH\) is inscribed in the circle. Calculate the magnitudes of the interior angles of the chordal quadrilateral \(HBCF\). (See the picture.)
\( \alpha=90^{\circ}\); \( \beta=112.5^{\circ}\); \( \gamma=90^{\circ}\); \( \delta=67.5^{\circ}\)
\( \alpha=90^{\circ}\); \( \beta=67.5^{\circ}\); \( \gamma=90^{\circ}\); \( \delta=67.5^{\circ}\)
\( \alpha=90^{\circ}\); \( \beta=122.5^{\circ}\); \( \gamma=80^{\circ}\); \( \delta=67.5^{\circ}\)
\( \alpha=90^{\circ}\); \( \beta=67.5^{\circ}\); \( \gamma=90^{\circ}\); \( \delta=112.5^{\circ}\)

2000005910

Level: 
B
The regular heptagon is inscribed in a circle. Calculate the magnitudes of the interior angles of the chordal quadrilateral \(ACEG\). (See the picture.)
\( \alpha=4\cdot\frac{360^{\circ}}{14}\); \( \beta=3\cdot\frac{360^{\circ}}{14}\); \( \gamma=3\cdot\frac{360^{\circ}}{14}\); \( \delta=4\cdot\frac{360^{\circ}}{14}\)
\( \alpha=4\cdot\frac{360^{\circ}}{7}\); \( \beta=3\cdot\frac{360^{\circ}}{7}\); \( \gamma=3\cdot\frac{360^{\circ}}{7}\); \( \delta=4\cdot\frac{360^{\circ}}{7}\)
\( \alpha=4\cdot\frac{180^{\circ}}{14}\); \( \beta=3\cdot\frac{180^{\circ}}{14}\); \( \gamma=3\cdot\frac{180^{\circ}}{14}\); \( \delta=4\cdot\frac{180^{\circ}}{14}\)
\( \alpha=4\cdot\frac{360^{\circ}}{14}\); \( \beta=4\cdot\frac{360^{\circ}}{14}\); \( \gamma=3\cdot\frac{360^{\circ}}{14}\); \( \delta=3\cdot\frac{360^{\circ}}{14}\)

2010012901

Level: 
B
Consider a circle \( k \) with radius \( 5\,\mathrm{cm} \). In the circle is inscribed a convex quadrilateral \( ABCD \) so that the diagonal \( AC \) is the diameter of the circle, the length of \( BC \) is \( 8\,\mathrm{cm} \), and the length of \( DC \) is \( 5\,\mathrm{cm} \). Determine the length of side \( AD \). (See the picture.)
\(5 \sqrt{3}\,\mathrm{cm} \)
\( 8\,\mathrm{cm} \)
\( 10\,\mathrm{cm} \)
\(3 \sqrt{5}\,\mathrm{cm} \)