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Question

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$^2$.

The correct answer is
$50\sqrt{2}$

To find the area of the shaded region \(PQRO\), we follow these steps:

  1. Given that points \(P, Q,\) and \(R\) lie on a circle with radius 10 cm, and \( \overline{PQ} = \overline{RQ} \), \( \triangle PQR\) is isosceles.
  2. The angle \( \angle PQR = 45^\circ \).
  3. Since \(PQ = RQ\) and \(QO\) is a bisector, the angle \(\angle PQO = \angle RQO = \frac{45^\circ}{2} = 22.5^\circ\).
  4. The line segments \(PQ\) and \(RQ\) are chords of the circle.
  5. Using the property that the sum of angles in a triangle is \(180^\circ\), we have: \(\angle POQ = 180^\circ - 45^\circ = 135^\circ\\)
  6. To find the area of \( \triangle POQ \) and \( \triangle ROQ \), use the formula for the area of a triangle: \(\text{Area} = \frac{1}{2} \times r^2 \times \sin(\theta)\) where \(\theta\) is the angle between the lines.
  7. Calculate the area of each sector:
    • The area of sector \(POQ = \frac{1}{2} \times 10^2 \times \sin(135^\circ) = 50\sin(135^\circ)\).
    • Since \(\sin(135^\circ) = \sin(180^\circ - 135^\circ) = \sin(45^\circ) = \frac{\sqrt{2}}{2}\), the area of sector \(POQ\) becomes \(50 \times \frac{\sqrt{2}}{2} = 25\sqrt{2}\) cm\(^2\).
    • The area of sector \(ROQ\) is equal to that of sector \(POQ\) due to symmetry: \(25\sqrt{2}\) cm\(^2\).
  8. The total area of \( \triangle PQRO \) is the area of both sectors: \(\text{Area} = 25\sqrt{2} + 25\sqrt{2} = 50\sqrt{2} \text{ cm}^2\).

Thus, the area of the shaded region \(PQRO\) is \(50\sqrt{2} \text{ cm}^2\).

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Important Questions from Mensuration and Geometry

  1. 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)
  2. 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)
  3. The volume of a sphere of diameter 1 unit is ______ than the volume of a cube of side 1 unit.
  4. 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 ______
  5. Right triangle PQR is to be constructed in the xy - plane so that the right angle is at P and line PR is parallel to the x-axis. The x and y coordinates of P, Q, and R are to be integers that satisfy the inequalities: $-4\le x \le 5$ and $6 \le y \le 16$. How many different triangles could be constructed with these properties?

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