AREAS RELATED TO CIRCLES

11 AREAS RELATED TO CIRCLES

Description

Quick Overview

This section discusses the concepts of sectors and segments of circles, detailing their areas and the formulas to calculate them.

Standard

In this section, students learn about the definitions and properties of sectors and segments of circles. The section introduces formulas for calculating the areas of these shapes, including the relationships between their components and provides examples to reinforce understanding.

Detailed

Areas Related to Circles

In this section, we delve into understanding the sector and segment of a circle. A sector of a circle is defined as the area enclosed by two radii and the arc connecting them, while a segment is defined as the area enclosed by a chord and the arc that connects its endpoints. We categorize sectors as minor and major based on the angle subtended at the circle's center, while a corresponding minor and major segment are defined similarly.

To calculate the area of a sector, we use the formula:

$$
\text{Area of sector} = \frac{ฮธ}{360} \times ฯ€r^2
$$

Here, \(ฮธ\) is the angle in degrees, and \(r\) is the radius of the circle. The length of the arc can also be determined with:

$$
\text{Length of arc} = \frac{ฮธ}{360} \times 2ฯ€r
$$

Next, to find the area of a segment, we subtract the area of the triangle formed by the two radii from the area of the corresponding sector:

$$
\text{Area of segment} = \text{Area of sector} - \text{Area of triangle}
$$

The section concludes with practical examples that illustrate these principles, fostering an understanding of how to apply these formulas in real-world contexts.

Key Concepts

  • Sector: The area formed between two radii and an arc.

  • Segment: The area formed between a chord and the arc it subtends.

  • Area of a Sector: Computed as \( \frac{ฮธ}{360} \times ฯ€r^2 \).

  • Area of a Segment: Area of sector minus area of the triangle formed.

Memory Aids

๐ŸŽต Rhymes Time

  • When you need to find, whatโ€™s between the lines, think sector and segment, the circleโ€™s designs.

๐Ÿ“– Fascinating Stories

  • Imagine a slice of pizza (representing a sector) and you take a bite out of it (creating a segment). You can calculate the remaining pizza area!

๐Ÿง  Other Memory Gems

  • SACS - Sectors Are Calculated Sectors: Sectors = \( \frac{ฮธ}{360} \times ฯ€r^2 \); Segments = Sector - Triangle.

๐ŸŽฏ Super Acronyms

S.A.S

  • Sectors And Segments to help remember their definitions and formulas.

Examples

  • To find the area of a sector with a radius of 4 cm and an angle of 30 degrees, we calculate it using the formula: Area = \( \frac{30}{360} \times ฯ€ \times 4^2 \approx 4.19 cm^2 \).

  • For a segment with a radius of 21 cm and an angle of 120 degrees, area can be found using: Area = Area of sector - Area of triangle.

Glossary of Terms

  • Term: Sector

    Definition:

    A portion of a circle enclosed by two radii and the arc between them.

  • Term: Segment

    Definition:

    A portion of a circle enclosed by a chord and the arc connecting its endpoints.

  • Term: Minor Sector

    Definition:

    The smaller sector formed by an angle less than 180 degrees.

  • Term: Major Sector

    Definition:

    The larger sector formed by an angle more than 180 degrees.

  • Term: Area of a Sector

    Definition:

    The size of a sector measured in square units, calculated as \( \frac{ฮธ}{360} \times ฯ€r^2 \).

  • Term: Area of a Segment

    Definition:

    The area defined by the segment of a circle, calculated as the area of the sector minus the area of the triangle.