Mathematical expressions
can be used in the following ways...

6

This mathematical expression
simply evaluates to the number 6.

-6

This is an example of
what is called 'unary minus'. It is used to represent negative
numbers.

10+5 ' This evaluates to 15

10-5 '
This evaluates to 5

10*5 '
This evaluates to 50

10/5 '
This evaluates to 2

5^3 '
This evaluates to 125 (5x5x5)

Mathematical expressions
can also be combined easily...

10*5-5/5 ' This evaluates
to 49

Brackets can also be used
to specify the order in which the calculation should be performed...

(10*5-5)/5 ' This evaluates
to 9

The answer is different
due to the part in brackets being done before everything else.