Distance is a measure in one dimension. By convention distance is always positive. If one takes a line and marks it off in equally spaced units, one can measure onedimensionally. A directed distance is a distance that can be positive or negative.
When describing multidimensional objects, such as rectangles (2dimensional) or solids (3dimensional), length is the measure of the longest dimension.
Width or breadth measure at right angles to the length. Height measures vertically at right angles to both length and width.
Abbreviation  Unit of Measure for Distance  Equals 

Metric System See also International System of Units.  
  micrometer  0.000001 m = 10^{6} m 
mm  millimeter  0.001 m = 10^{3} m 
cm  centimeter  0.01 m = 10^{2} m 
  decimeter  0.1 m = 10^{1} m 
m  meter  1 m 
  decameter  10 m = 10^{1} m 
  hectometer  100 m = 10^{2} m 
km  kilometer  1000 m = 10^{3} m 
  megameter  1000000 m = 10^{6} m 
gm  gigameter  1000000000 m = 10^{9} m 
English System  
in or "  inch  1/12 ft ≈ 0.0254m 
ft or '  foot  1 ft ≈ 0.3048m 
yd  yard  3 ft ≈ 0.9144m 
mi  mile  5280 ft ≈ 1609.344m 
Table 1: Units of Measure. 

Two points that are the same distance from a reference point are said to be equidistant from each other. When distance is taken to be positive, the distance from point A to point B is the same as the distance from point B to point A. 


The calculation of the distance from one point to another point uses the distance formula where and are the coordinates of the two points. 

The distance from point C to a line AB is defined as the shortest distance from the point to any point on the line. The shortest distance is found by constructing a new line, say CD that passes through point C perpendicular to line AB. So the first thing to do when calculating the distance from a point to a line is find the equation of this line. The slope of the new line CD is equal to the reciprocal of the slope of line AB. You can use the pointslope form of a line to find the equation of the line CD. Once the equation of line CD is found, find the coordinates of the
intersection of line AB and CD, which is point D.
Since the coordinates of D are the solution of the linear system containing
line Once the coordinates of D have been calculated, all that is left to do is find the distance from C to D. Use the algorithm for the distance between two points. 

The distance between lines make sense only for lines that are always the same distance apart. This means that the distance between lines only makes sense for parallel lines. The distance from line AB to a line CD is defined as the shortest distance from a point on CD to any point on the line AB. After selecting an arbitrary point on CD, follow the algorithm for finding the distance between a point and a line. 
#  A  B  C  D 
E  F  G  H  I 
J  K  L  M  N 
O  P  Q  R  S 
T  U  V  W  X 
Y  Z 
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