As shown in the figure, the circumference of the bottom surface of a cylinder is 20cm, the height AB is 4cm, and BC is the diameter of the upper bottom surface. An ant starts from point a, crawls along the side of the cylinder to point C, and the shortest distance is Why is ad half the circumference after unfolding? Isn't ad the diameter of a circle?

As shown in the figure, the circumference of the bottom surface of a cylinder is 20cm, the height AB is 4cm, and BC is the diameter of the upper bottom surface. An ant starts from point a, crawls along the side of the cylinder to point C, and the shortest distance is Why is ad half the circumference after unfolding? Isn't ad the diameter of a circle?

In fact, the shortest path is the length of the oblique side of a right triangle
(between two points, the shortest line segment)
One right side of the triangle is ad, which is half the perimeter of the bottom,
The other corner is the height of the cylinder
Remember to expand the side to understand

A cylinder with a height of 10 cm is evenly divided into two parts with equal volume and shape along the diameter of the bottom surface. The surface area of the cylinder is increased by 120 square cm
How many cubic centimeters is the product

The increase of surface area is two rectangles, area = 2 × diameter × height = 2 × diameter × 10 = 120 square centimeter
Diameter = 120 / 20 = 6cm
Radius = 3 cm
The volume of cylinder is 3.14 × 3 × 3 × 10 = 282.6 cubic centimeter

How much is the surface area of a cylinder with a base perimeter of 25.12cm and a height of 50cm sawed into two ends with a height of 25cm more than the original surface area of 100.48
Hand in

(1) 25.12 * 50 + 100.48 = 1356.48 (cm2)
A: its surface area is 1356.48 square centimeters