Figure 2, 9 corners, 2 right angles

It is proved that HL can be used when the right triangle is congruent. If the hypotenuses of two triangles are equal in length and one right-angled side is equal, then two right-angled triangles are congruent. Theorem: The hypotenuse and a right angle correspond to the congruence of two right triangles.

If two lines intersect and the product of their slopes is negative reciprocal, they are vertical. In a triangle, if the midline of one side is equal to half of the side where the midline is located, then the triangle is a right triangle.

Extended data:

The intersection of the bisectors of a (1) triangle is called the center of the triangle. It is the center of the inscribed circle of a triangle, and its distance to each side is equal.

The center of the circumscribed circle of a triangle, that is, the outer center, is the intersection of the perpendicular lines of the three sides of the triangle, and its distances to the three vertices are equal.

(2) The intersection of the three center lines of a triangle is called the center of gravity of the triangle, and its distance to each vertex is equal to twice its distance to the midpoint of the opposite side.

(3) The intersection of three heights of a triangle is called the vertical center of the triangle.

(4) The midline of the triangle is parallel to the third side and equal to half of the third side.

Baidu encyclopedia-right triangle