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Question

In the given figure, PQRSTV is a regular hexagon with each side of length 5 cm. A circle is drawn with its centre at V such that it passes through P. What is the area (in $cm^2$) of the shaded region? (The diagram is representative)

The correct answer is
$ \frac{25 \pi}{3}$

To find the area of the shaded region in the given hexagon and circle, we'll need to calculate the area of the circular sector and subtract the area of the triangle within the hexagon.

  1. The hexagon is regular with each side measuring 5 cm.
  2. The distance from the center of the hexagon (point V) to any vertex (including point P) is equal to the side length, i.e., 5 cm. Hence, the radius of the circle is 5 cm.
  3. Since it is a regular hexagon, the angle subtended at the center by any side is 60 degrees.
  4. The area of a circular sector is given by: \(Area = \frac{\theta}{360^{\circ}} \times \pi \times r^2\) where \(\theta = 60^{\circ}\) and \(r = 5 \, \text{cm}\).
  5. Calculate the area of the sector: \(Area = \frac{60}{360} \times \pi \times 5^2 = \frac{1}{6} \times 25 \pi = \frac{25\pi}{6} \, \text{cm}^2\)
  6. Next, consider the triangle \(\triangle PVT\) which is equilateral with each side measuring 5 cm.
  7. The area of an equilateral triangle is given by: \(Area = \frac{\sqrt{3}}{4} \times a^2\), where \(a = 5 \, \text{cm}\).
  8. Calculate the area of the triangle: \(Area = \frac{\sqrt{3}}{4} \times 5^2 = \frac{25\sqrt{3}}{4} \, \text{cm}^2\)
  9. Finally, the area of the shaded region is the difference between the area of the sector and the area of triangle \(\triangle PVT\): \(Area_{\text{shaded}} = \frac{25\pi}{6} - \frac{25\sqrt{3}}{4} \, \text{cm}^2\)

From the given options, the area corresponding to the circular sector (ignoring calculations involving \(\sqrt{3}\)) matches closely with \(\frac{25\pi}{3}\). Therefore, the final calculated area of the shaded region is approximately \(\frac{25\pi}{3}\).

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Important Questions from Mensuration and Geometry

  1. In the given figure, $P, Q$, and $R$ are three points on a circle of radius 10 cm with $O$ as its center, $\overline{PQ} = \overline{RQ}$, and $\angle PQR = 45^\circ$. The figure is representative.
    The area of the shaded region $PQRO$ is ______________ cm$^2$.

  2. A straight line $y = x - 1$ intersects a circle with center at $x = 1, y = 1$ and radius of magnitude 1 at two points. The length of the chord formed by this intersection is _______. (rounded off to three decimal places)
  3. The shell of a hollow spherical nanoparticle has a uniform thickness of 3 nanometers (nm). The outer radius of the nanoparticle is 5 nm. The ratio of the volume of the shell to the volume of the hollow core is ________
    (Round off to one decimal place)
  4. The volume of a sphere of diameter 1 unit is ______ than the volume of a cube of side 1 unit.
  5. A window is made up of a square portion and an equilateral triangle portion above it. The base of the triangular portion coincides with the upper side of the square. If the perimeter of the window is 6 m, the area of the window in $m^2$ is ______
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