How to use auxiliary lines skillfully in mathematics for senior high school entrance examination. What else can be made into a circle, an arc, a double length and an intercept? I don't know when and how to use it. Look for patterns in various bodies.

Second, in the bisector of the angle, the distance from the bisector of the angle to the vertical on both sides of the angle.

3. In a triangle, make parallel lines of center line, height, center line and side.

Fourth, in the parallelogram, find the intersection of diagonals.

Verb (abbreviation of verb) Trapezoid: (1) Make two heights: make two heights AE and DF from both ends of the upper bottom, and divide the trapezoid into a rectangle and two triangles.

⑵ Translating the waist: Draw a parallel line of the waist from a vertex of the trapezoid and divide the trapezoid into parallelogram and triangle.

⑶ Lengthening the waist: Lengthening the intersection of the two waists at one point, turning the trapezoidal problem into a triangular problem.

(4) Translating diagonal lines: parallel lines passing through one end of the upper bottom in a diagonal form form form a parallelogram;

5] Other methods:

A, when the waist midpoint of a trapezoid is known, an congruent triangle is often formed through the midpoint.

B when the midpoint of the two waists in a trapezoid is known, it is often used as the center line of the trapezoid.

Sixth, in the circle, calculate the chord, radius, chord center distance, center distance and so on. , pay attention to the construction of similar triangles, so that the corresponding proportion, and then calculate the required number; If necessary, use Pythagorean theorem to solve it.

Seven, in the circle, to prove the tangent, you need to connect the radius to prove the perpendicular, or use other methods that you are more skilled.

The above is a summary, and the details need to be reflected in specific issues. You should study it carefully!

I wish you good grades in the senior high school entrance examination!