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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, PQRS is a square of side 2 cm and PLMN is a rectangle. The corner L of the rectangle is on the side QR. Side MN of the rectangle passes through the corner S of the square.
    What is the area (in cm²) of the rectangle PLMN?
    Note: The figure shown is representative.

  2. A regular dodecagon (12-sided regular polygon) is inscribed in a circle of radius $r$ cm as shown in the figure. The side of the dodecagon is $d$ cm. All the triangles (numbered 1 to 12) in the figure are used to form squares of side $r$ cm and each numbered triangle is used only once to form a square.
    The number of squares that can be formed and the number of triangles required to form each square, respectively, are:
    Note: The figure shown is representative.

  3. Which one of the following options has the correct sequence of objects arranged in the increasing number of mirror lines (lines of symmetry)?
  4. A circle with center at $(x, y) = (0.5, 0)$ and radius $= 0.5$ intersects with another circle with center at $(x, y) = (1, 1)$ and radius $= 1$ at two points. One of the points of intersection $(x, y)$ is:
  5. During a half-moon phase, the Earth-Moon-Sun form a right triangle. If the Moon-Earth-Sun angle at this half-moon phase is measured to be $89.85^{\circ}$, the ratio of the Earth-Sun and Earth-Moon distances is closest to
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