LZ said to learn in the third grade, only after class:

The lower p is the half circumference and s is the area.

Similarly, the area of a quadrilateral inscribed in a circle is S=√(p-a)(p-b)(p-c)(p-d).

Angular bisector theorem, upstairs said,

Median line theorem: If AD is the median line of △ABC, then AB 2+AC 2 = 2 (AD 2+BD 2).

Inscribed circle formula: r=S÷p

Circumcircle formula: R=abc÷4S

Cosine theorem: Let the included angle between A and B in a triangle be ∠C, then C 2 = A 2+B 2-2AB× COS ∠ C C.

Sine theorem: a: b = sin ∠ a: sin ∠ b

Let the included angle between A and B be C, then S=( 1/2)ab×sinC.

Seva's theorem: in triangle ABC, if AD, BE and CF intersect at point O, then (AF/FB )× (BD/DC )× (CE/EA) =1.

Each midline of a triangle is divided into 1: 2 by other midlines.

Theorem of circle;

The circle is inscribed with the diagonal sum of the quadrilateral 180,

Chord tangent angle theorem: let AB be the chord in the circle and l be the tangent line passing through a, then the included angle between l and AB = the circumferential angle of ab's team,

Cyclic power theorem;

(1) intersection chord theorem: If two chords AB and CD intersect at point P on the circle, then PA×PB=PC×PD,

(2) Secant Theorem: Change the (1) point P inside the circle to outside the circle.

(3) Tangent Theorem: As a special case of (2), if the straight line PC is tangent to the circle, then PA× Pb = PC 2.

Well, that's probably all for junior high school.

The landlord wants more QQ to find me,