Explanation:
Proportionality (mathematics)
In mathematics,
two variable quantities are proportional if one of them is
always the product of the other by
a constant quantity, called the coefficient of proportionality,
or the proportionality constant. In other words, x and y are proportional
if the ratio is constant. We also say that one
of the quantities is proportional to the other.
For example, if the speed of an object
is constant, it travels a distance proportional to the travel time.
Symbol
The mathematical symbol '∝' is used to indicate that two values are proportional. For
example, A ∝ B.
Direct
proportionality
Given two variables x and y, y
is (directly) proportional to x (x and y vary
directly, or x and y are in direct variation)
if there is a non-zero constant k such that
The relation is often denoted
and the constant ratio
is called the proportionality
constant or constant of proportionality.
(Our solved example in mathguru.com uses
this concept)
Examples
1. If an
object travels at a constant speed,
then the distance traveled is proportional to the time spent
traveling, with the speed being the constant of proportionality.
2. The circumference of a circle is proportional to its diameter, with the constant of
proportionality equal to π.
3. On a map drawn
to scale, the distance between
any two points on the map is proportional to the distance between the two
locations that the points represent, with the constant of proportionality being
the scale of the map.
4. The force acting on a certain object due to gravity is proportional to the object's mass; the constant of proportionality
between the mass and the force is known as gravitational
acceleration.
http://en.wikipedia.org/wiki/Proportionality_(mathematics)
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