The side view of a cylinder is square. The ratio of diameter to height of the bottom of the cylinder is () A. 2π：1B. 1：1C. 1：πD. π：1

The side view of a cylinder is square. The ratio of diameter to height of the bottom of the cylinder is () A. 2π：1B. 1：1C. 1：πD. π：1

Let the diameter and height of the bottom of the cylinder be D and h respectively, then π d = h, so D: H = 1: π

As shown in the figure, it is a cylinder, its height is 20cm, and the circumference of its bottom surface is 42cm. If an ant wants to climb from point a on the bottom surface of the cylinder along the curved surface of the cylinder to the upper ground B opposite to a, find out the length of the shortest route of crawling?

If you cut the cylinder from the line AB, it's a rectangle. Is the trajectory the diagonal of the rectangle
Then the length of Pythagorean root with 20 square plus 42 square OK~

A cylinder is 24 cm high. If the height is reduced by 3 cm, its surface area will be reduced by 18.84 square cm. What is the surface area of the original cylinder?

The reduced surface area is the side area, so the perimeter of the bottom surface is 18.84 △ 3 = 6.28 cm, the radius is 6.28 △ 3.14 △ 2 = 1 cm, so the original surface area is 1 × 1 × 3.14 × 2 + 6.28 × 24 = 157 square cm