1, triangle: A figure composed of three line segments that are not on the same line end to end is called a triangle. A new definition of old knowledge.
2. Trilateral relationship: the sum of any two sides of a triangle is greater than the third side, and the difference between any two sides is less than the third side. Used to judge the existence of a triangle and find the range of the third side or perimeter.
3. Height: Draw a vertical line from the vertex of the triangle to the line where the opposite side is located, and the line segment between the vertex and the vertical foot is called the height of the triangle. High lines are difficult to draw, especially the height on the two short sides of an obtuse triangle, which is also a big test site. The intersection of three heights of a bell triangle is outside the triangle, the intersection of heights of a right triangle is on the triangle, and the height of an acute triangle is inside the triangle.
4. midline: in a triangle, the line segment connecting the vertex and its relative midpoint is called the midline of the triangle. The center line bisects the area of the triangle, so it is easy to choose the fill-in-the-blank question.
5. Angular bisector: The bisector of the inner angle of a triangle intersects the opposite side of this angle, and the line segment between the vertex and the intersection of this angle is called the angular bisector of the triangle. (Chapter 12 also focuses on the nature of the angular bisector, and only a simple logical relationship is needed here).
6. The sum of the interior angles of the triangle is 180. The proof process deserves careful scrutiny, especially the method of adding auxiliary lines, which can provide theoretical basis for doing geometry problems in the future.
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Mathematics [English: Mathematics, from ancient Greece μ? θξμα(máthēma)； Often abbreviated as math or maths], it is a discipline that studies concepts such as quantity, structure, change, space and information.
Mathematics is a universal means for human beings to strictly describe and deduce the abstract structure and mode of things, and can be applied to any problem in the real world. All mathematical objects are artificially defined in essence. In this sense, mathematics belongs to formal science, not natural science. Different mathematicians and philosophers have a series of views on the exact scope and definition of mathematics.
Mathematics plays an irreplaceable role in the development of human history and social life, and it is also an indispensable basic tool for studying and studying modern science and technology.