What is the ratio of diameter to radius and length in the same circle

What is the ratio of diameter to radius and length in the same circle

Two to one

The radius of a circle changes from 2 cm to 3 cm, and the area of the circle increases by () square cm

Small circle area: 2 * 2 * 3.14 = 12.56cm2 (4 π)
Large circle area: 3 * 3 * 3.14 = 28.26cm2 (9 π)
28.26-12.56=15.7cm2 （5π）

The radius of a circle is doubled and the surface area is increased by 24 square meters. How many square centimeters is the original area of the circle

Double the radius
Area expansion
2 × 2 = 4 times
Area increase
4-1 = 3 times
It turns out that the area of this circle is
24 △ 3 = 8 square centimeter