Кафедра: Математика

Usually, when drawing a triangle, we draw one side horizontally. This side is usually called the base. There is nothing special about the base. By turning your paper you can make any side into the base. There is no mathematical reason to call one side a base; we do it to make talking about the triangle easier. When you have a triangle and think of one of the sides as the base, then there is one corner of the triangle that is not on the base and this point is the furthest point on the triangle from the base. The height of the triangle is the line that is perpendicular to the base and goes through that furthest point. Sometimes instead of being called the height it is called the altitude of the triangle. The length of the base and the height are the only two numbers you need to know when calculating the area of any triangle. Just multiply base and height and divide by and you have the area of the triangle!

The perimeter of the triangle is easy: just add up all the sides you have the perimeter. You can multiply one side of an equilateral triangle by three as well. As for isosceles triangles, simply multiply one of the equal sides by two and add the shorter one.

Quadrilaterals

A quadrilateral is a shape with four sides. They can be classified into many different categories:

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  Parallelograms are shapes where opposite sides and angles are equal. The opposite sides are parallel, hence the name.
  
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    Rectangles are parallelograms where the angles are all 90°. Its width or breadth refers to the shorter sides, while its length refers to its longer ones.
    
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    Rhombuses are parallelograms where all the sides are equal, and opposite angles are equal.
    
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    Squares are parallelograms that are both rectangles and rhombuses, i.e. all angles are right and all sides are equal.
    
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  Trapeziums have two opposite sides that are parallel. The parallel sides are sometimes called the upper and lower bases.
  
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