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# geometry of 2D

### Geometry of 2D shapes

Term | Definition |
---|---|

Area | The number of square units needed to cover a given surface |

Trapezoid | A quadrilateral with exactly one pair of parallel sides |

Perimeter | The distance around a polygon |

Circumference | The distance around a circle |

Surface Area | The sum of the areas of the faces or surfaces of a three-dimensional figure |

Prism | A polyhedron that has two congruent polygon shaped bases and other faces that are parallelograms |

Volume | The number of cubic units needed to fill a given space |

Parallelogram | A quadrilateral with two pairs of parallel sides |

Diameter | A line segment that passes through the center of a circle and has end-points on the circle or the length of that segment |

Radius | A line segment with one end-point at the center of a circle and the other end-point on the circle or that length of the segment |

area of a rectangle | length x width |

area of a parallelogram | base x height |

area of a trapezium | ((a +b) x h)/2 |

area of a circle | 3.142 x radius x radius |

Area of a triangle | A = (b x h) divided by 2 |

Circumference of circle | Pi x d |

Perimeter of a rectangle (and parallelograms) | A = 2(L x W) |

Triangle Area = | 1/2 x base x perpendicular height |

Square Area = | base x base |

Rectangle Area = | base x height |

Parallelogram Area = | base x perpendicular height |

Trapezium Area = | 1/2 x height x (top + bottom) |

Circle Area = | π x r squared |

Area (rhombus) | bxh |

Acute Triangle | A triangle with 3 acute angles |

Right Triangle | A triangle that has a 90 degree angle (right angle) |

Obtuse Triangle | A triangle with one angle that is greater than 90 degrees. |

Square | Four equal sides and four right angles |

Rhombus | A parallelogram with four equal sides |

Trapezoid(US)/Trapezium(UK) | A quadrilateral with exactly one pair of parallel sides |

Pentagon | 5 sided polygon |

Octagon | 8-sided polygon |

Nonagon | 9 sided polygon |

Decagon | 10 sided polygon |

Heptagon | 7 sided polygon |

Hexagon | 6 sided polygon |