Cara Mencari Keliling dan Luas Lingkaran Jika Jari-jari dan Diameter Diketahui

Summary

In this educational video, the presenter teaches how to calculate the circumference and area of a circle. Using simple formulas, viewers learn how to apply them based on whether the radius or diameter is provided. The video offers clear examples, such as a circle with a radius of 28 cm and a diameter of 24 cm, explaining how to calculate both the circumference and area step-by-step. The use of different values for Pi (22/7 or 3.14) depending on the measurement helps reinforce key concepts in circle geometry, making it easy to understand and apply in various scenarios.

Takeaways

• 😀 The video introduces the concept of finding the circumference and area of a circle.
• 😀 To find the circumference, the formula used is 2 * π * r, where 'r' is the radius of the circle.
• 😀 If the radius is a multiple of 7, π is approximated as 22/7. Otherwise, 3.14 is used for π.
• 😀 For the example with a radius of 28 cm, using π as 22/7 gives a circumference of 176 cm.
• 😀 To find the area of a circle, the formula is π * r^2, where 'r' is the radius.
• 😀 In the example with a radius of 28 cm, using π as 22/7 gives an area of 2464 cm².
• 😀 When given the diameter of a circle, the formula for the circumference is π * d, where 'd' is the diameter.
• 😀 For the example with a diameter of 24 cm, using π as 3.14 gives a circumference of 75.36 cm.
• 😀 The formula for the area of a circle with a known diameter is 1/4 * π * d².
• 😀 In the example with a diameter of 24 cm, using π as 3.14 gives an area of 452.16 cm².
• 😀 The video emphasizes that calculating the circumference and area of a circle is simple once the radius or diameter is known.

Q & A

What is the formula for calculating the circumference of a circle when the radius is known?

The formula for calculating the circumference of a circle when the radius is known is: Circumference = 2 * π * r, where r is the radius of the circle.

What value of π should be used when the radius is a multiple of 7?

When the radius is a multiple of 7, the value of π to be used is 22/7.

How do you simplify the formula for circumference when the radius is 28 cm?

When the radius is 28 cm, we use π = 22/7. Then, simplify the equation: 2 * (22/7) * 28. Divide 28 by 7 to get 4, then multiply: 2 * 22 * 4 = 176 cm for the circumference.

What is the formula for calculating the area of a circle when the radius is known?

The formula for calculating the area of a circle when the radius is known is: Area = π * r^2, where r is the radius of the circle.

What value of π is used when the radius is not a multiple of 7?

When the radius is not a multiple of 7, the value of π used is approximately 3.14.

How do you calculate the area of a circle with a radius of 28 cm?

To calculate the area, use the formula: Area = π * r^2. Using π = 22/7 and r = 28 cm, simplify the equation: (22/7) * 28 * 28 = 2464 cm² for the area.

What is the formula for finding the circumference when the diameter is known?

When the diameter is known, the formula for finding the circumference is: Circumference = π * d, where d is the diameter.

What happens when the diameter is not a multiple of 7 for calculating the circumference?

When the diameter is not a multiple of 7, the value of π used is 3.14. For example, when the diameter is 24 cm, the circumference is calculated as 3.14 * 24 = 75.36 cm.

How do you calculate the area of a circle when the diameter is known?

To calculate the area when the diameter is known, use the formula: Area = (1/4) * π * d^2, where d is the diameter. For example, when the diameter is 24 cm, the area is 452.16 cm².

Why is 24 divided by 4 in the formula for calculating the area with the diameter?

In the area formula for a circle with diameter, (1/4) * π * d^2, we first divide the diameter by 4 to simplify the calculation before multiplying with π and d².