A true proposition is a correct proposition, that is, if the topic of the proposition is established, then the conclusion must be established. For example:

① Two parallel lines are cut by a third straight line, and their internal angles are equal.

② if a > b and b > c, then a > C ..

③ The vertex angles are equal.

Axiom is a correct proposition that people have summed up in long-term practice. There is no need to prove it by other methods. The main axiom we learned in the first geometry is:

There is a straight line through two points, and there is only one straight line.

② There is one and only one straight line parallel to this straight line at a point outside the straight line.

(3) congruent angles are equal and two straight lines are parallel.

④ Two straight lines are parallel and have the same angle.

A proposition can be written in this format: if+conditions, then+conclusions.

Propositions with contradictory conditions and results are false propositions, such as:

The sum of the three internal angles of a triangle is not equal to 180 degrees.

People can fly.

In addition, if the conclusion does not fully meet the conditions (there are special cases that meet the conditions but do not meet the conclusions), it is also a false proposition, such as:

A quadrangle is a square (quadrangle includes a square but not only a square, but also a rectangle, a trapezoid and so on). ).