Objective : To find solution sets of equations over a given domain.
An equation is formed by placing an equals sign between two numerical or variable expressions, called the sides of the equation.
Sentences containing variables (like the equations 5x - 1 = 9 and y + 2 = 2 + y) are called open sentences. The given set of numbers that a variable may represent is called the domain of the variable.
A variable in an equation can be replaced by any of the numbers in its domain. The resulting equation may be either true or false.
You may use braces { } to show a set of numbers. A short way to write "the set whose member are 1, 2, and 3" is {1, 2, 3}.
Example 1
The domain of x is {1, 2, 3}.
Is the equation 5x - 1 = 9 true when x = 1? when x = 2? when x = 3?
In example 1, when x replaced by 2, the resulting equation is true. Any value of a variable that turns an open sentence into a true statement is a solution, or root, of the sentence and is said to satisfy the sentence.
The set of all solutions of an open sentence is called the solution set of the sentence. Finding the solution set is called solving the sentence. In Example 1, there is only one solution. For the equation 5x - 1 = 9 you may say either "The solution is 2", or "The solution set is {2}".
Some equations have more than one solution, and some equations have no solutions. The sentence y + 2 = 2 + y is true no matter what number is substituted for y. Therefore the solution set is the set of all number. If you are asked to solve the equation over the domain {0, 1, 2, 3}, you state that the solution set is the domain itself, {0, 1, 2, 3}.
Here is another way to show that the domain of a variable y is {0, 1, 2, 3} :
(Read "y belongs to the set whose members are 0, 1, 2, and 3.")
Example 2
Example 3
Solve over the domain {6, 8, 12} :
Five more than twice a number is 29. What is the number ?
By : Mr. Danielz