This Winter Olympics is hosted by Beijing and hosted by Zhangjiakou. Choosing Zhangjiakou instead of the northeast where the temperature is lower has a lot to do with the temperature besides the distance. Previous Winter Olympics are usually held in February, and the temperature-17℃ ~ 10℃ is the most ideal temperature.
Trajectory of ski jumping: Parabolic frog princess Gu Ailing's third jump, such as the assistant speed of skaters, can reach 24 meters per second. When the skater slides, we will see a beautiful parabola, and its trajectory can be abstracted as a quadratic function image.
Set classification:
Union set: The set whose elements belong to A or B is called the union (set) of A and B, marked as A∪B (or B∪A), and pronounced as A and B (or B and A), that is, A∪B={x|x∈A, or X.
For example, the complete works U = {1, 2,3,5} A = {1,3,5} B = {1,2,5}.
Their two sets contain four elements: 1, 2, 3, 5, regardless of the number of times the elements appear, as long as the elements appear in these two sets. Then say a ∪ b = {1, 2, 3, 5}. The shaded part is a ∩ B.