Divided by sides: equilateral triangle isosceles triangle equilateral triangle

Similar triangles: Judgment of Triangle with Equal Corresponding Angles and Proportional Corresponding Sides similar triangles: 1, Equal Corresponding Angles 2, Proportional Corresponding Sides 3, Proportional Corresponding Sides 4. A triangle composed of a straight line parallel to a triangle and the other two sides of the triangle is similar to this triangle.

Congruent triangles: similar triangles with a similarity ratio of 1 is a special case of similar triangles. Congruent triangles's judgment: 1, three corresponding sides are equal, 2, two angles are equal and any side is equal, 3, a right triangle with any side is congruent.

Pythagorean theorem: the sum of squares of two right angles of a right triangle is equal to the square of the hypotenuse.

The relationship between three sides of a triangle: the sum of any two sides must be greater than the third side, and the difference between any two sides must be less than the third side.

The sum of the three internal angles of a triangle is equal to 180.

The height of the opposite side of the vertex of an isosceles triangle is on the same line as the bisector of the angle formed by the center line and the vertex.

The two base angles of an isosceles triangle are equal and the two waists are equal.

An equilateral triangle has three equal triangles, all of which are equal to 60. The height of an equilateral triangle is 3 0.5 times the length of its side.

The area of a triangle is equal to the base times the height divided by two.

Trigonometric function: sine (sin) cosine (cos) tangent (tan) cotangent (cot)

SinA= side of angle A divided by hypotenuse cosA= adjacent side of angle A divided by hypotenuse tanA= opposite side of angle A divided by adjacent side of angle A cotA= adjacent side of angle A divided by opposite side of angle A.

(Sina) 2+(COSA) 2 =1Sina = Tana * Cosata Na = 1/ Kota.