Math Problem Statement

OWX is a sector of a circle with a radius of 34 cm. OYZ is a sector of a circle with a radius of 23 cm. The central angle of both sectors is 75°. Work out the area of the shaded shape WXYZ. Give your answer in cm² to 1 d.p.

Solution

To solve this problem, we need to find the area of the shaded region WXYZWXYZ. The shaded area is the difference between the areas of the two sectors, one with a radius of 34 cm (sector OWXOWX) and the other with a radius of 23 cm (sector OYZOYZ).

Step 1: Formula for the Area of a Sector

The formula for the area AA of a sector with radius rr and angle θ\theta (in degrees) is given by: A=θ360×πr2A = \frac{\theta}{360} \times \pi r^2 where:

  • rr is the radius of the sector,
  • θ\theta is the central angle in degrees,
  • π\pi is approximately 3.14159.

Step 2: Area of Sector OWXOWX (radius = 34 cm, angle = 75°)

AOWX=75360×π×(34)2A_{\text{OWX}} = \frac{75}{360} \times \pi \times (34)^2 AOWX=75360×π×1156A_{\text{OWX}} = \frac{75}{360} \times \pi \times 1156 AOWX0.2083×3.14159×1156A_{\text{OWX}} \approx 0.2083 \times 3.14159 \times 1156 AOWX757.92cm2A_{\text{OWX}} \approx 757.92 \, \text{cm}^2

Step 3: Area of Sector OYZOYZ (radius = 23 cm, angle = 75°)

AOYZ=75360×π×(23)2A_{\text{OYZ}} = \frac{75}{360} \times \pi \times (23)^2 AOYZ=75360×π×529A_{\text{OYZ}} = \frac{75}{360} \times \pi \times 529 AOYZ0.2083×3.14159×529A_{\text{OYZ}} \approx 0.2083 \times 3.14159 \times 529 AOYZ346.36cm2A_{\text{OYZ}} \approx 346.36 \, \text{cm}^2

Step 4: Shaded Area WXYZWXYZ

The shaded area is the difference between the two sector areas: Ashaded=AOWXAOYZA_{\text{shaded}} = A_{\text{OWX}} - A_{\text{OYZ}} Ashaded=757.92346.36A_{\text{shaded}} = 757.92 - 346.36 Ashaded411.56cm2A_{\text{shaded}} \approx 411.56 \, \text{cm}^2

Thus, the area of the shaded shape WXYZWXYZ is approximately 411.6 cm² (rounded to 1 decimal place).

Would you like further details or have any questions?

Relative Questions:

  1. How do we calculate the circumference of a sector?
  2. What is the relationship between a sector's area and its central angle?
  3. How would the solution change if the central angle was 90° instead of 75°?
  4. Can the formula for a sector's area be extended to radians? How?
  5. What if one sector was only partially shaded—how would you approach that calculation?

Tip:

For any geometric problem involving sectors, always ensure that the angle is in degrees or radians and is used correctly in formulas for area or arc length.

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Math Problem Analysis

Mathematical Concepts

Geometry
Circle
Sector Area

Formulas

Area of a sector = (θ / 360) × π × r²

Theorems

Area of a sector

Suitable Grade Level

Grades 8-10