1) Using equations, you will are able to predict data from a specific value of independent variable. You can see how does the independent variable affect the dependent variable.
2) If x = 1 then 2 + 1 = 5 is false. If x = 3 then 2 + 3 = 5 is true. Thus, we can say that the mathematical sentence containing the variable becomes either true or false depending upon the value of the variable. This type of sentence is called an open sentence, thus 2 + x = 5 is an open sentence.
