Equilateral triangle has three equal sides and angles of 60°. It is the most symmetrical triangle with 3 lines of reflection. Area and perimeter formulas are derived using Pythagorean theorem
Equilateral triangle has three equal sides and angles. It is a special case of isosceles triangle with base. All internal angles are 60°. Area formula is half base multiplied by height
Acute triangle has three acute angles (less than 90°). Obtuse triangle has one obtuse angle (greater than 90°) and two acute angles. No Euclidean triangle can have more than one obtuse angle
A right angle is exactly 90 degrees or π/2 radians. Right angles form when a ray's endpoint is on a line. Term comes from Latin "angulus rectus" meaning "upright"
Two geometric objects are perpendicular if their intersection forms right angles at a foot. Perpendicularity extends to lines, planes, and segments. Perpendicularity is symmetric, meaning perpendicular lines are always parallel
Trapezoid is a 4-sided shape with two parallel bases. Area formula: A = ½(b1+b2)h. Add base lengths together to find total base length. Multiply base length by height to get area. Divide total area by 2 to get final result