Triangle Cheat Sheet

Key Definitions

• Triangle: A polygon with three edges and three vertices.

• Vertices: Points where two sides meet.

• Base: Any one of the sides of the triangle, often the bottom side.

• Height: Perpendicular distance from the base to the opposite vertex.

Important Concepts

Types of Triangles

• Equilateral: All sides and angles are equal (60° each).

• Isosceles: Two sides are equal, and the angles opposite these sides are equal.

• Scalene: All sides and angles are different.

• Right Triangle: One angle is exactly 90°.

Properties

• The sum of interior angles = 180°.

• The longest side is opposite the largest angle.

Key Formulas

• Area of Triangle:

• Perimeter of Triangle:

• Pythagorean Theorem (Right Triangle):

Common Mistakes to Avoid

Common Mistake: Forgetting that the sum of angles in a triangle is always 180°.

Memory Tricks

Tip: "EIS" — Equilateral, Isosceles, Scalene — types of triangles.

Key Diagrams

      A
     / \
    /   \
   /     \
  B-------C

• A: Vertex opposite the base.

• B & C: Other vertices.