For example, when a worker makes a circular cover with mortar, he only has a small stick (the length is equal to the radius of the required circle). Rotate the stick once with one end of the stick as the center, and the figure swept by the stick is a circle. From this point of view, I inspire students to define a circle from the perspective of motion: the graph obtained by rotating a line segment around its endpoint is a circle. Then inspire students to think: Why are these covers (including the manhole covers we see every day) usually round? For this problem, students generally think it is a good cover, but the fundamental reason for its good cover lies in the nature of the circle: the radius of the same circle is equal, the circle is a central symmetrical figure and an axisymmetric figure, and its symmetrical axis has countless lines, thus abstracting the theory from reality and explaining the reality with theory, which deepens students' understanding and application of knowledge.

In fact, there are still many problems that need to be solved by mathematics in the construction of this project, such as the relationship between the height of greenhouse vents and the incident angle of sunlight, the relationship between illumination and close planting, and the relationship between close planting and yield, which have given us profound enlightenment in mathematics teaching. Teaching should not be satisfied with solving book knowledge, but should go to life and solve practical problems with what you have learned, so that everyone can learn "useful mathematics" and cultivate students' ability to solve problems. That's all that matters.

Analysis: Because there are 12 months in a year, assuming that each student's birthday month is different, then only 12 is enough, and two other people's birthdays must be the same as one of the previous 12 people's birthdays, so at least two students in this group have birthdays in the same month.

Note: This example is a practical problem related to our life. When solving this problem, we use analytical methods, which is what we should learn in mathematics. It's not the same as the arithmetic calculation in primary school!