just a number
Value
When a given set of values for the variables are substituted in the expression the result is the value of the expression.
In a boolean algebraic expression if the ^ is replaced by v and v replaced by ^ then that becomes dual of that boolean expression.
x+5, but the x can be replaced with any variable (i.e. letter)
They are replaced as letters.
no
A variable is a letter that represents a number. An expression that contains at least one variable is called variable expression, also called algebraic expression. A variable expression has one or more terms. A term is a number, a variable, or a product of numbers and variables. For example,3(x^2)y + 2xy + x - 7 is a variable expression, where you have 4 terms.When working with variable expression, you often use the substitution principle:If a = b, then a may be replaced by b in any expression.The set of numbers that a variable may be represent is called replacement set, or domain, of the variable. To evaluate a variable expression, you replace each variable with one of its values and simplify the numerical expression that results.Example: Evaluate the expression 2x - 4y for x = 5 and y = -9.Solution:2x - 4y= 2(5) - 4(-9)= 10 + 36=46
substitution
The same as in many other expressions. It is a variable, that is, it can be replaced by any number.
If the equal sign in a linear equation in two variables is replaced with an inequality symbol, the result is a linear inequality in two variables. 3x-2y>7 x<-5
In a perturbed system, writing the equations of motion in a form where the contribution of fast variables is replaced by their average on the corresponding invariant torus.
X is a variable which can be replaced with virtually anything ranging from -infinity to +infinity, imaginary numbers, other variables and even whole other functions.