When you put the number in place of the variable (like maybe the 'x' or the 'y') wherever the variable occurs in the equation, and the statement you get out of all the numbers you have is not true, then you know the number is not a solution.
before
variable
A variable
That's a dependent variable, I believe.
A variable must be in place of a number, or representing a range of possible values. Otherwise, it is a constant and so yous imply replace it with the value of that constant.
variable
A variable.
a variable
The unknown or the variable
Yes, it is.
A letter that is used in place of a number is called a variable.