Base side

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In elementary geometry, a side of a triangle or certain quadrilaterals is called the base or base line .

Base of an isosceles triangle.
  • In the case of an isosceles triangle , the base side (also called the base ) is the side on which the two same angles are applied: The other two sides must be of the same length and are referred to as the legs of the isosceles triangle. In the case of an equilateral triangle, any side can therefore be referred to as the “base side”.
  • In graphic representations, the "lower" side of a polygon is often referred to as the base side .
  • When calculating the area of a triangle, the length of one side must be multiplied by the length of the height perpendicular to it and the product halved. The side that is used here is called the “base side” in this context.
  • For some special rectangles, the area can be calculated in a similarly simple manner. Examples are:
    • Rectangle: area is width times height, sometimes formulated as a motto: "base times height",
    • Parallelogram: area is base times height.

When calculating the area of ​​a triangle or certain quadrilaterals, one calls any side as the base side because it is used in a certain way for the calculation. This side does not have to have any special properties in the figure. The choice of the base side is often linked to the orientation of the figure in a drawing.

See also