First, the basic properties of the triangle:

1. The sum of two sides is greater than the third side, and the difference between the two sides is less than the third side; Three sides of an equilateral triangle are equal; The waist of an isosceles triangle is equal.

2. The sum of the three internal angles is equal to 180 degrees;

3. Three acute triangles with internal angles less than 90 degrees;

A right triangle has one angle equal to 90 degrees, and the sum of the other two angles is equal to 90 degrees;

The inner angle of an obtuse triangle is greater than 90 degrees;

Three internal angles of an equilateral triangle are equal, and each angle is equal to 60 degrees;

The base angles of isosceles triangles are equal.

2. Angle relation of triangle (theorem):

1. Right triangle: hook, chord and chord theorem, i.e.

Square of hypotenuse = square of short right angle+square of long right angle.

Median Theorem: Median line of hypotenuse = half of hypotenuse.

(The line between the midpoint of the hypotenuse and the vertex of the right angle-the hypotenuse centerline)

2. Arbitrary (oblique) triangle:

The midpoint line between two sides of a triangle is parallel to the third side and equal to half of the third side.

Let a, b and c be three sides corresponding to three internal angles, respectively, and then there are:

A) sine theorem:

a/sinA=b/sinB=c/sinC=2R

Where r is the radius of the circumscribed circle of the triangle.

B) cosine theorem:

a^2=b^2+c^2-2b*c*conA

b^2=a^2+c^2-2a*c*conB

c^2=a^2+b^2-2a*b*conC

C) tangent theorem:

Tg [(a-b)/2] = [(a-b)/(a+b)] * TG (c/2), or

(A-B)/(A+B)= TG[(A-B)/2]/TG[(A+B)/2]

In physics, n here stands for Newton, the unit of force.

1n = 10 (-3) stein = 10 5 dynes = 102 * 10 (-3) kg weight = 102 g weight.