Some classical triangle centers are:
The medians of a triangle are the line segments created by joining one vertex to the midpoint of the opposite side. Since every triangle has three sides and three angles, it has three medians (ma, mb and mc).
Centroid theorem: the distance between the centroid and its corresponding vertex is twice the distance between the barycenter and the midpoint of the opposite side. That is, the distance from the centroid to each vertex is 2/3 the length of each median. This is true for every triangle.
An altitude of a triangle (ha, hb y hc) is a perpendicular line segment from a vertex to the opposite side. This line containing the opposite side is called the extended base of the altitude.
Altitude can also be understood as the distance between the base and the vertex.
Where is the Orthocenter of a Triangle Located?
- If it’s an obtuse triangle the orthocenter is located outside the triangle (as we see in the picture above).
- If it’s an acute triangle the orthocenter is located inside the triangle.
- If it’s a right triangle the orthocenter lies on the vertex of the right angle.
The circumcenter of a triangle (O) is the point where the three perpendicular bisectors (Ma, Mb y Mc) of the sides of the triangle intersect. It can be also defined as one of a triangle’s points of concurrency.
The perpendicular bisector of a triangle is a line perpendicular to the side that passes through its midpoint.
It’s possible to find the radius (R) of the circumcircle if we know the three sides and the semiperimeter of the triangle.
The radius of the circumcircle is also called the triangle’s circumradius.
The formula for the circumradius is:
Where is the Circumcenter of a Triangle Located?
- If it’s an obtuse triangle the circumcenter is located outside the triangle (as we see in the picture above).
- If it’s an acute triangle the circumcenter is located inside the triangle.
- If it’s a right triangle the circumcenter lies on the midpoint of the hypotenuse (the longest side of the triangle, that is opposite to the right angle (90°). We can see an example in the figure below.
See the Thales’ Theorem.
The radius (or inradius) of the incircle is found by the formula:
Where is the Incenter of a Triangle Located?
Euler’s Theorem: Distance between Incenter and Circumcenter of a triangle
Can we calculate the distance between these two centers of a triangle?
Remember that the incenter (I) is the center of the incircle, which is the largest circle that will fit inside the triangle. The incircle’s radius is called inradius (r). While, the circumcenter (O) is the center of the circumscribed circle, or circumcircle, whose circumradius (R) is equal to the distance between the circumcenter and any of the three vertices of the triangle.
So, we can calculate the distance between incenter (I) and circumcenter (O) using Euler’s Theorem, which states that the distance between the incenter and circumcenter of a triangle can be calculated by the equation:
Where OI is the distance between both centers, and R and r are the length of circumradius and inradius respectively.
See the picture below:
In an equilateral triangle all three centers are in the same place.
The relative distances between the triangle centers remain constant.
Distances between centers:
AUTHOR: Bernat Requena Serra