Ôn tập Toán 11 sách Chân trời sáng tạo - Chương 4-Bài 2: Hai đường thẳng song song

Vietnamese document discusses various aspects of geometry, including the properties of incenter and angles related to triangle side lengths. The paper focuses on proving several geometric theorems.

Sinh viên, nhà nghiện cứu toán học và những người có sở thích về toán.

The scholarly Vietnamese document is devoted to exploring essential concepts in geometry and presenting proofs for various theorems. The primary focus lies on analyzing the properties of an incenter within a triangle, as well as connections between angles and triangle side lengths. To begin with, the paper introduces the incenter of a triangle, demonstrating that it is located at the midpoint of the line segment connecting the midpoints of each side of the triangle. The proof utilizes the definition of the incenter and properties related to medians of a triangle. Following this, the document moves on to discuss another theorem stating that the angle between two medians of a triangle is equal to one-third of the angle subtended by the corresponding side at the incenter. This conclusion relies on the fact that the medians of a triangle divide it into three congruent triangles with equal angles and sides. Next, the paper delves into an analysis of another pair of angles related to triangle side lengths. Specifically, the document discusses a theorem stating that the angle between two altitudes of a triangle is half of the angle subtended by the corresponding base at the opposite vertex. The proof involves considering the symmetry properties of the geometric figure and utilizing the relationships between angles and lines parallel to the base of the triangle. Finally, the paper presents yet another theorem connecting the lengths of two triangles with the same base and altitude: if a point lies on both triangles' medians, then it divides each median into the ratio of 2:3 for the corresponding triangle sides. This result is derived from the properties of the incenter and medians within a triangle. Overall, this scholarly Vietnamese document offers valuable insights into various aspects of geometry and presents comprehensive proofs to support its findings.