How to prove that two straight lines are perpendicular?

A: There are many methods. 1, the most basic method is to prove that the angle formed by the intersection of two lines is a right angle;

2. Using the inverse theorem of Pythagorean theorem, it is proved that the square of the opposite side of an angle is equal to the sum of the squares of the other two sides in a triangle.

3. Using the "three lines in one" of the isosceles triangle, it is proved that if one of the two lines is the bottom of the isosceles triangle and the other is the bisector of the top angle of the isosceles triangle or the middle line or height on the bottom, the last two lines are perpendicular to each other;

4. It is proved that the sum of two acute angles of a right triangle is equal to 90 from the theorem of the sum of internal angles of a triangle, so two triangles with complementary acute angles must be right triangles;

5. Prove that the diagonals of diamonds are perpendicular to each other. If it can be proved that the second line is the diagonal of a diamond, it is perpendicular to each other;

6. Inference by using the theorem of circumferential angle: It is proved that the included angle between two straight lines is the circumferential angle opposite to the diameter of a circle, so it must be a right angle; 7. Using the relationship between the sides of a triangle, as long as it is proved that the length of one side of the triangle is half that of the other side, then the triangle must be a right triangle of 30.

8, vector method, the product of two vectors = 0;

9. Analytic method, product of slopes of two straight lines =- 1.