One or nine kilometers:
1, there is only one straight line between two points.
2. The line segment between two points is the shortest.
3. The complementary angles of the same angle or equal angle are equal.
4. The complementary angles of the same angle or equal angle are equal.
5. There is one and only one straight line perpendicular to the known straight line.
6. Of all the line segments connecting a point outside the straight line with points on the straight line, the vertical line segment is the shortest.
7. Parallel axiom? After passing a point outside the straight line, there is one and only one straight line parallel to this straight line.
8. If two straight lines are parallel to the third straight line, the two straight lines are also parallel to each other.
9. The internal dislocation angles are equal, the internal angles on the same side are complementary, the complementary angles are equal, and the two lines are parallel.
Second, three important thoughts:
1, the idea of "equation"
The so-called "equation" idea means that for mathematical problems, especially the complex relationship between unknown quantities and known quantities encountered in reality, we are good at constructing relevant equations from the viewpoint of "equation" and then solving them.
2. The idea of "combination of numbers and shapes"
Pay attention to the thinking training of "combination of numbers and shapes". Any problem, as long as it is a little close to the "shape", should draw a sketch to analyze according to the meaning of the problem. This is not only intuitive, but also comprehensive, easy to find the breakthrough point, which is of great benefit to solving problems.
3. The concept of "correspondence"
For example, when calculating or simplifying, we will correspond the left side of the formula, a and b, and then directly get the result of the original formula with the right side of the formula, that is, we will use the idea and method of "correspondence" to solve the problem.
The second and third grades will also see the one-to-one correspondence between points on the number axis and real numbers, the one-to-one correspondence between points on the rectangular coordinate plane and a pair of ordered real numbers, and the correspondence between functions and their images.
Extended data:
"Axiom", in traditional terms, refers to a self-evident assumption in many branches of science. On the basis of various scientific fields, there may be some unconfirmed and accepted additional assumptions, which are called "postulates".
Axioms exist in many branches of science, but the postulates in each branch of science are different. The validity of postulate must be based on real-world experience.
The traditional practice is well described in the Elements of Geometry, which gives some postulates (geometric common sense facts summarized from people's experience) and some "axioms" (extremely basic and self-evident assertions). The correctness of the axiom has been proved in practice and is also recognized by everyone. No other proof is needed, and it can be used as the basis for proving other true propositions.
References:
Baidu encyclopedia-true proposition
Baidu encyclopedia-axiom
Baidu Encyclopedia-Equation Thinking