Triangle is a closed shape with 3 sides, 3 angles, and 3 vertices. Sum of all interior angles in a triangle is 180°. Triangle inequality states two sides plus two sides equals third side. Side opposite greater angle is longest side
A 30-60-90 triangle is a special right triangle with angles 30°, 60°, and 90°. The angles are in a ratio of 1:2:3. The sides are in the ratio of 1:√3:2
Centroid is the arithmetic mean position of all points on a figure's surface. Term "centroid" coined in 1814, replacing "center of gravity". Centroid coincides with barycenter in uniform mass density cases
Bisection divides something into equal or congruent parts using a bisecting line. Segment bisector passes through midpoint, angle bisector through apex. In three dimensions, bisection uses bisecting plane
Right triangle has two perpendicular sides forming a 90-degree angle. Opposite side is called hypotenuse, adjacent sides are called legs. Every right triangle is half of a rectangle divided along its diagonal
Right triangle has one 90-degree internal angle. Hypotenuse is longest side opposite right angle. Other two sides are called legs