The first lecture

The principle of parallel lines bisecting line segments

Proportional theorem of dividing two parallel lines into line segments

Judgement and nature of three similar triangles.

1. similar triangles's judgment

2. The nature of similar triangles

Projective Theorems of Four Right Triangle (Emphasis)

The second lecture (main points)

Rounded corner theorem

Properties and Judgement Theorem of Quadrilateral Inscribed by Two Circles

Properties and Judgement Theorem of Tri-circle Tangent

Properties of Quadrant Tangent Angle

Five proportional line segments related to a circle.

The third lecture (no lecture)

parallel projection

Secant between two planes and cylindrical surface

Secant lines of three planes and conical surfaces

Teachers only talk about the first two chapters, and they are required to learn and master similar triangles, similarity ratio and projective theorem. Straight lines and circles are the key points! The test is generally to find the length of the line segment and prove that the equation is established.