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Geometry Notes
Types of Angles
1. Acute- less than 90°
2. Obtuse- more than 90 °
3. Right- exactly 90°
4. Straight- exactly 180°
Triangles (classified by sides) (always classify by sides unless directions ask otherwise)
1. Equilateral:
 All sides are congruent (equal length)
 All angles are congruent (equal degree measurement- 60°)
 3 lines of symmetry
2. Isosceles:
 2 sides are congruent (equal length)
 2 angles are congruent (equal degree measurement)
 1 line of symmetry
3. Scalene:
 No sides are congruent (no equal lengths)
 No angles are congruent (no equal degree measurements)
 No lines of symmetry
Triangles (classified by sides angles) (only classify by angles if directions ask you to)
1. Right:
 One 90° angle
2. Acute:
 Three acute angles (all less than 90°)
3. Obtuse:
 One obtuse angle (more than 90°)
 You can never have more than one obtuse
angle in a triangle
Quadrilaterals (all of the following shapes are quadrilaterals; these shapes have four sides)
1. Parallelogram:
 Opposite sides are parallel
 Opposite sides are congruent (equal length)
 Opposite angles are congruent (equal angle measurements)
2. Rectangle:
 Four right angles (all angles measure 90°)
 Parallelogram
3. Square:
 All four sides are congruent (equal lengths)
 Four right angles (all angles measure 90°)
 Rectangle
 Parallelogram
4. Rhombus:
 Opposite angles are congruent (equal angle measures)
 All sides are congruent (equal lengths)
 Parallelogram
 May be a square
5. Trapezoid:
 One pair of parallel lines
6. Kite:
 2 pairs of congruent sides
 No parallel lines
Polygons (Shapes with 3 or more straight sides that meet)
Regular polygons: all sides and angles are congruent; these are the shapes we are used to seeing
1. Triangle
 3 sides
6. Octagon
 8 sides
2. Quadrilateral
 4 sides
7. Nonagon
 9 sides
3. Pentagon
 5 sides
8. Decagon
 10 sides
4. Hexagon
 6 sides
9. Undecagon
 11 sides
5. Heptagon
 7 sides
10. Dodecagon
 12 sides