The two focal points (or foci, sometimes called locus or loci) are both on the major axis, and equal distances away from the centre. The two points where the minor axis crosses the circumference are called the co-vertices. The four points where the axes cross the circumference are called the vertices (singular vertex). The longer axis is called the major axis the shorter axis is the minor axis. The arc (a section of the circumference of the circle - see below) and a chord - the straight line joining the two ends of the arc.Īn ellipse has two main axes, and is symmetrical around them. Pie charts are made up of a number of sectors relating in size to the data they show.Ī sector can be any size, however a sector that is half a circle (180°) is called a semicircle, while a quarter circle sector (90°) is called a quadrant.Ī segment is the curved part of a sector, the part that is left if you remove the triangle from a sector. Sectors are shaped like a slice of pizza, with a curved edge and each straight side the same length as the radius of the circle, or pizza, from which it was cut. Sectors and segments are 'slices' of a circle. This formula is usually abbreviated to πr 2 For more about area, see our page Calculating Area. The area of a circle is equal to π × radius 2. The circumference of a circle is equal to π x diameter, or 2 × π × radius (abbreviated to 2πr). Π is important because it is used to calculate the circumference and the area of a circle. Π has a value of 3.142 (although as it is infinite, this is an approximation of its exact value). In mathematics, it is used to represent a particular constant, which is also an irrational or infinite number (see our page on Special Numbers for more).
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