In mathematics,
inequalities
compare numbers and
expressions that are
not equal to
one another.
Generally, the
following symbols
are used for
comparison:
,
,
,
.
Each of these
symbols compares the
relative size of two
numbers
to show which number
is bigger, and which
number is
smaller.
Inequalities
are important
because they are
common to
everyday life
experiences.
People
intuitively use the
concept of
inequality to
compare options and
make choices based
on relative
value.
For example, a
person may ask
themselves:
"Can I buy a
new car with $10,000
if a new car costs
$11,000?" The
comparison of these
choices is an
inequality. One
number is smaller
than the other
number.
Automatic control
systems rely on this
concept as well. A
thermostat uses an
inequality
(comparing
temperatures) to
decide whether to
turn on a heater or
air conditioner. For
example, the
thermostat may turn
on an air
conditioner when the
temperature rises
above 85 degrees (or
turn off the air
conditioner when the
temperature falls
below 80
degrees).
The
Properties of
Inequality
of Real Numbers 
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Reversal
Property of
Inequality

The Reversal
Property of
Inequality
states that
an
inequality
(the entire
expression)
can be
reversed
without
affecting the
validity of the
expression.
When an
inequality sign
is reversed,
the expressions
and the right
and left hand
side of the
inequality sign
trade places.
The expression
on the right is
placed on the
left hand side
of the
inequality
symbol, and the
expression on
the left is
placed on the
right hand side
of the
inequality
symbol.
Examples
follow.
a =
any real
number,
b =
any real
number
If a
b,
then
b
a
If a
b,
then
b
a
If a
b,
then
b
a
If a
b,
then
b
a
If 5
1,
then
1
5
If x + 3
y,
then
y
x +
3
If Jim
weighs more
than Frank,
then Frank
weighs less
than
Jim.