Make a line segment equal to the known line segment, make an angle equal to the known angle, make the bisector of the middle vertical line of the known line segment pass a little, make a known angle of the vertical line, make an isosceles triangle with two known angles, make a known angle of the triangle, and make two triangles.

Principles are proved theorems, such as bisecting the angle, using the edge axiom.

The principle that the distance between two points at the intersection of a circle centered on a fixed point and any point on the bisector of an angle is equal to two points (it is easy to prove that this is a congruent triangles).

Drawing public law

The following are the basic methods that can be used in ruler drawing, also known as graphic method. Any step of ruler drawing can be decomposed into the following five methods:

A straight line can be drawn through two known points.

Known center and radius can be used as a circle.

If two known straight lines intersect, the intersection point can be found.

If a known straight line intersects a known circle, the intersection point can be found.

If two known circles intersect, the intersection can be found.

Make a circle after three o'clock, know three points: A, B, C, and find the circle after three o'clock. Practice 1 Connect AB and AC; ② Make the midpoint D and E of line AB and AC respectively; ③ The vertical line crossing D is AB, the vertical line crossing E is AC, and the two vertical lines intersect at O; ④ A circle with O as the center and OA length as the radius is the circle to be found.

Regular triangles whose vertices are on three parallel lines are called parallel lines L 1, L2 and L3. Finding positive △ABC makes the three vertices fall on three parallel lines respectively. Method 1: Take any point D in L 1 as the vertex and make a regular triangle △DBE, so that B and E fall on L2 (a simple method in which the dotted line is a regular triangle); (2) In C, a straight line intersection L3 of d and e is made; ③ Take B as the center and BC as the radius, make an arc intersection point L 1 in A, and connect A, B and C into △ABC.

Method 2: ① Take any point B of L2 as the common vertical line of three parallel lines, intersecting L 1 in E and L3 in D; ② the perpendicular l4 of the line segment EB; ③ Make a straight line DG crossing D to make ∠ EDG = 30, crossing L4 to G; ④B intersects G as a straight line, and intersects L 1 at A; ⑤ Take B as the center, BA as the radius, make an arc intersection L3 with C, and connect A, B and C into △ABC.

Pictures can be found in the examples in Resources.

Hope to adopt, O(∩_∩)O Thank you.