It is called a variable.
X is the symbol for multiplication, as in 2X2=4 X (or any other letter) is often used to represent an unknown quantity.
If a quantity does not have a direction, its a scalar quantity, not a vector quantity.
Since pi is an irrational number it is impossible to represent the exact quantity as a decimal; you can only give and approximate value. However, if you write a fraction that includes the symbol for pi, you are giving an exact quantity.
A variable is assigned to represent an unknown quantity.
x or any other variable
A variable
Variable
It is called a variable.
It is called a variable.
veribal
element symbol
element symbol
In maths the symbols x and n are usually used to represent an unknown quantity. These may be referred to as a variable.
The quantity symbol for reactance is X.
The triangle symbol that means change is called the delta symbol. It is commonly used in mathematics and science to represent a change in quantity or variable.
The symbol for the base quantity of time is "t".