How do you convert diameter to radius?

To convert diameter to radius, divide the diameter by 2: $$r = \\frac{d}{2}$$ .

What is the area of a circle with a diameter of 12?

First, find the radius: $$r = \\frac{12}{2} = 6$$ . Then, use the area formula: $$A = \\pi (6)^2 = 36\\pi \\approx 113.10$$ .

What is the relationship between radius and area?

The area of a circle increases with the square of the radius: if the radius doubles, the area increases by a factor of four.

If the area of a circle is 78.50, what is the radius?

Using the area formula, solve for r: $$r = \\sqrt{\\frac{A}{\\pi}} = \\sqrt{\\frac{78.50}{\\pi}} \\approx 5$$ .

What is the circumference of a circle?

The circumference is the distance around the circle, given by the formula: $$C = 2\\pi r$$ .

If the radius of a circle is 4, what is the circumference?

Using the formula $$C = 2\\pi r$$ , the circumference is $$C = 2\\pi (4) = 8\\pi \\approx 25.13$$ .

What happens to the area if the radius is tripled?

If the radius is tripled, the area increases by a factor of nine, since area is proportional to the square of the radius.

Area of Circles Flashcards

Student preview

15 questions

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1.

FLASHCARD QUESTION

Front

What is the formula for the area of a circle?

Back

2.

FLASHCARD QUESTION

Front

What is the value of π (pi)?

Back

π (pi) is approximately equal to 3.14.

3.

FLASHCARD QUESTION

Front

What is the radius of a circle?

Back

The radius of a circle is the distance from the center of the circle to any point on its circumference.

4.

FLASHCARD QUESTION

Front

If the radius of a circle is 6, what is the area?

Back

5.

FLASHCARD QUESTION

Front

What is the diameter of a circle?

Back

6.

FLASHCARD QUESTION

Front

If the diameter of a circle is 10, what is the radius?

Back

The radius is half of the diameter, so if the diameter is 10, the radius is 5.

7.

FLASHCARD QUESTION

Front

What is the area of a circle with a radius of 10?

Back

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