An irregular shape is a shape which has sides and angles of any length and size. A square, by definition, is a regular shape: it is, in fact, a regular rectangle. A regular triangle is called an equilateral triangle. This is when children will compare and order angles in preparation for using a protractor and compare lengths and angles to decide if a polygon is regular or irregular. In Year 5 , pupils distinguish between regular and irregular polygons based on reasoning about equal sides and angles.
In Year 6 , pupils compare and classify geometric shapes based on their properties and sizes and find unknown angles in any triangles, quadrilaterals, and regular polygons. Each side of the pentagon is the same length. Is the shape a regular pentagon? Explain your answer. Use a ruler to draw a regular hexagon on this circle. Wondering about how to explain other key maths vocabulary to your children? Check out our Primary Maths Dictionary , or try these other maths terms:.
Drawing 2D shapes. What are the names of 2D and 3D shapes? Count the sides of 2D shapes. Mystery 3D shape net. Properties of 3D shapes. What are regular and irregular shapes? Regular and irregular polygons. Children are taught to name common 2D shapes including polygons such as squares, rectangles, triangles, pentagons, hexagons and octagons. Children will be taught to identify properties of shapes such as the number of sides and vertices corners.
Children will extend their knowledge of polygons to include different types of triangles and quadrilaterals. Children are taught to compare lengths and angles of polygons to decide if they are regular or irregular. Children will be taught to distinguish between regular and irregular polygons based on reasoning about equal sides and angles. Regular Polygon A regular polygon 's sides are all of the same length and its angles are the same size. For example, a square is a regular polygon.
Examples of regular polygons are shown below. Irregular Polygon If a polygon is not a regular polygon, then it is said to be an irregular polygon. For example, the quadrilateral shown below is an irregular polygon. It is common for some dimensions not to be shown for more complex shapes. In such cases missing dimensions can be calculated. The missing horizontal length can be calculated. Take the shorter horizontal known length from the longer horizontal known length.
The simplest and most basic polygon for the purposes of calculating area is the quadrilateral. To obtain the area, you simply multiple length by vertical height. For parallelograms, note that vertical height is NOT the length of the sloping side, but the vertical distance between the two horizontal lines. This is because a parallelogram is essentially a rectangle with a triangle cut off one end and pasted onto the other:.
You can see that if you remove the left-hand blue triangle, and stick it onto the other end, the rectangle becomes a parallelogram. The area is length the top horizontal line multiplied by height, the vertical distance between the two horizontal lines. To work out the area of a triangle , you multiple length by vertical height that is, the vertical height from the bottom line to the top point , and halve it. This is essentially because a triangle is half a rectangle.
To calculate the area of any regular polygon , the easiest way is to divide it into triangles, and use the formula for the area of a triangle. See our page Calculating Area for more, including examples. See our Introduction to Trigonometry page for more information. Continue to: Calculating Area Curved Shapes.
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