The radius of a circle is 5cm. If the radius is doubled, the diameter will be doubled, the circumference will be doubled, and the area will be doubled Just expand () times, is () square centimeter?

The radius of a circle is 5cm. If the radius is doubled, the diameter will be doubled, the circumference will be doubled, and the area will be doubled Just expand () times, is () square centimeter?

The radius of a circle is 5cm. If the radius is increased by 2 times, the diameter will be increased by (2) times to (20) cm, the circumference of the circle will be increased by (2) times to (62.8) cm, and the area will be increased by (4) times to (314) square cm

The radius of a circle is r, which is three times the radius of the other circle. What is the sum of the circumference and the area of the two circles

The sum of circumference:
3.14×2×r+3.14×2×(r÷3)
=3.14×2(1+1÷3)×r
=8.37×r
=8.37r
Area sum:
3.14×r×r+3.14×(r÷3)×(r÷3)
=3.14×(1+1÷9)×r×r
≈3.488×r×r
=3.49r ^ 2 (the square of R)

The radius of the big circle is 10 cm and the radius of the small circle is 4 cm. What is the ratio of the circumference of the big circle to that of the small circle______ What's the area ratio______ ．

The perimeter of the big circle: the perimeter of the small circle = (3.14 × 2 × 10): (3.14 × 2 × 4) = 5:2, the area of the big circle: the area of the small circle = (3.14 × 102): (3.14 × 42) = 100:16, = 25:4; answer: the perimeter ratio of the big circle and the small circle is 5:2, the area ratio is 25:4