How do you find the radius if you know the area of a circle?

Use the formula: $$r = \sqrt{\frac{A}{\pi}}$$ .

What is the area of a semi-circle with a radius of 4 inches?

$$A = \frac{1}{2} \pi (4)^2 = 8\pi \approx 25.13 in^2$$ .

What is the perimeter of a semi-circle with a diameter of 10 inches?

$$P = \frac{1}{2} \pi d + d = \frac{1}{2} \pi (10) + 10 \approx 15.71 in$$ .

What is the area of a quarter circle with a radius of 6 inches?

$$A = \frac{1}{4} \pi (6)^2 = 9\pi \approx 28.27 in^2$$ .

If a circle has an area of 50 cm², what is the radius?

$$r = \sqrt{\frac{50}{\pi}} \approx 3.99 cm$$ .

What is the circumference of a circle with a radius of 3 meters?

$$C = 2\pi(3) = 6\pi \approx 18.85 m$$ .

How do you convert circumference to diameter?

Use the formula: $$d = \frac{C}{\pi}$$ .

What is the area of a circle with a diameter of 10 cm?

$$A = \pi (\frac{10}{2})^2 = 25\pi \approx 78.54 cm^2$$ .

Circumference and Area of Circles Flashcards

Student preview

15 questions

Show all answers

1.

FLASHCARD QUESTION

Front

What is the definition of circumference?

Back

The distance around a circle.

Tags

CCSS.7.G.B.4

2.

FLASHCARD QUESTION

Front

What is the definition of area in relation to a circle?

Back

The space inside the circle.

3.

FLASHCARD QUESTION

Front

What is the formula for finding the circumference of a circle?

Back

Tags

CCSS.7.G.B.4

4.

FLASHCARD QUESTION

Front

What is the formula for finding the area of a circle?

Back

Tags

CCSS.7.G.B.4

5.

FLASHCARD QUESTION

Front

If the radius of a circle is 5 cm, what is its area?

Back

Tags

CCSS.7.G.B.4

6.

FLASHCARD QUESTION

Front

If the circumference of a circle is 31.4 cm, what is the diameter?

Back

Tags

CCSS.7.G.B.4

7.

FLASHCARD QUESTION

Front

What is the relationship between diameter and radius?

Back

Tags

CCSS.7.G.B.4

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