Center of gravity: the three midlines of a triangle intersect at one point, which is called the center of gravity of the triangle; Sagging center: the three heights of a triangle or their extension lines intersect at a point, which is called the sag center of the triangle; Inner heart: the center of the inscribed circle of a triangle is called the inner heart, and the distance from the outer center to the three sides of the triangle is equal; Outer center: The center of the circumscribed circle of a triangle is called the outer center, which is also the intersection of the perpendicular lines of three sides, and the distance from the outer center to the three vertices of the triangle is equal.