1. A circle is an axisymmetric figure, and every straight line passing through the center of the circle is its axis of symmetry.

2. Addition and subtraction of mathematical scores: addition and subtraction of fractions with the same denominator and addition and subtraction of numerator with the same denominator. Fractions with different denominators are divided into fractions with the same denominator and then added and subtracted.

Congruent triangles: A triangle with the same shape and size is called congruent triangles. Congruent triangles is a special case of similar triangles.

4. The straight line parallel to one side of the triangle intersects with other two sides or extension lines of both sides, and the triangle formed is similar to the original triangle.

5. The right triangle is divided into two right triangles by the height on the hypotenuse, which is similar to the original right triangle, and the two right triangles are similar.