2. Perimeter of triangle: Given the length of three sides, find the perimeter of triangle.
3. Properties of isosceles triangle: Know the length of the base and vertex of isosceles triangle, and find the height on the base.
4. Properties of right triangle: Know the two right angles of right triangle, and find the length of hypotenuse.
5. Application of Pythagorean Theorem: Knowing the two right angles of a right triangle, find the length of the hypotenuse.
6. Sum of internal angles of triangle: Given three internal angles of triangle, find the sum of these three angles.
7. Application of Helen's formula: Know the length of three sides of a triangle and find its area.
8. The problem of judging the type of triangle: Given the length of three sides, judge whether this triangle is an equilateral triangle, an isosceles triangle, a right triangle or a general triangle.
9. Triangle Similarity: It is known that the proportions of the three groups of corresponding sides of two triangles are equal, so find out whether these two triangles are similar.
10. The problem of the circumscribed circle of a triangle: Given the three vertices of the triangle, find the radius of the circumscribed circle of the triangle.
1 1. The problem of the inner center, the outer center and the vertical center of a triangle: Given the three vertices of the triangle, find the coordinates of the inner center, the outer center and the vertical center of the triangle.
12. Tangent problem of triangle: Given a vertex and a tangent point of triangle, find the equation of this tangent.
13. The problem of the triangle's center of gravity: Given the three vertices of the triangle, find the coordinates of the triangle's center of gravity.
14. Triangle midline problem: Knowing two vertices of a triangle, find the equation of the triangle midline.
15. area comparison of triangles: given four triangles with different shapes, how to compare their areas?