Cara Menghitung LUAS dan KELILING Lingkaran

Circle Basics: Circumference and Area

The video explains the basic parts of a circle, how to calculate its circumference and area, and works through two examples before giving a practice problem.

Circle Elements and Symbols

• Center: The point in the middle of the circle, labeled O in the diagram.
• Radius ((r)): A line from the center to a point on the circle.
• Diameter ((d)): A line across the circle that passes through the center. The diameter is twice the radius:
  • (d = 2r)
  • (r = \frac{d}{2})

The Value of (\pi)

The presenter uses either:

• (\pi = \frac{22}{7}) when the radius is a multiple of 7
• (\pi = 3.14) when it is not

Circumference and Area

• Circumference is the length around the outside of a circle.
• Area is the amount of space inside a circle.

Formulas

• Circumference using the radius: (C = 2\pi r)
• Circumference using the diameter: (C = \pi d)
• Area: (A = \pi r^2), or (\pi \times r \times r)

Worked Examples

1. Radius = 28 cm

Since 28 is a multiple of 7, use (\pi = \frac{22}{7}).

• Circumference: (2 \times \frac{22}{7} \times 28 = 176) cm
• Area: (\frac{22}{7} \times 28 \times 28 = 2{,}464) cm²

2. Diameter = 8 cm

First, find the radius: (8 \div 2 = 4) cm. Using (\pi = 3.14):

• Circumference: (3.14 \times 8 = 25.12) cm
• Area: (3.14 \times 4^2 = 50.24) cm²

Remember to use square units when expressing area.

Practice Problem

Calculate the circumference and area of a circle with a diameter of 14 cm.

Speaker and Source

The video features one unnamed presenter or instructor speaking on a learning channel. Subtitles refer to the channel inconsistently as “arfee” and “RW”; the video metadata identifies it as Ruang Belajar Channel.