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. The parallel axiom passes through a point outside the straight line, and there is 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 same angle is equal, and two straight lines are parallel.

10, internal dislocation angles are equal, and two straight lines are parallel.

1 1, the inner angles on the same side are complementary, and the two straight lines are parallel.

12, two straight lines are parallel and have the same angle.

13, two straight lines are parallel and the internal dislocation angles are equal.

14. Two straight lines are parallel and complementary.

15, the sum of two sides of a theorem triangle is greater than the third side.

The basic nature of proportion:

If a:b=c:d, then ad=bc.

If ad=bc, then a: b = c: d.

(2) Comprehensive performance:

If a/b=c/d, then (a b)/b = (c d)/d.

(3) Equidistant attribute:

If a/b=c/d=…=m/n(b+d+…+n≠0),

Then (a+c+…+m)/(b+d+…+n) = a/b.

The midline theorem of trapezium The midline of trapezium is parallel to the two bottoms and equal to half of the sum of the two bottoms L = (a+b) ÷ 2s = l× h.

Diamond area = half of diagonal product, that is, S=(a×b)÷2.

Proportional theorem of dividing parallel lines into line segments Three parallel lines cut two straight lines, and the corresponding line segments are proportional.

A circle is a set of points whose distance from a fixed point is equal to a fixed length.

The interior of a circle can be regarded as a collection of points whose center distance is less than the radius.

The outside of a circle can be regarded as a collection of points whose center is farther than the radius.

The same circle or the same circle has the same radius.

The distance to the fixed point is equal to the trajectory of the fixed length point, which is a circle with the fixed point as the center and the fixed length as the radius.

The locus of a point whose distance is equal to the two ends of a known line segment is the median vertical line of the line segment.

The locus of a point with equal distance to both sides of a known angle is the bisector of this angle.

The locus of a point with equal distance to two parallel lines is a straight line parallel to these two parallel lines and with equal distance.

The judgment theorem of tangent passes through the outer end of the radius, and the straight line perpendicular to this radius is the tangent of the circle.