## BJP4 Self-Check 4.28: quadraticPreconditions

Author: Marty Stepp (on 2016/09/08)

Exercise 3.8 asked you to write a method called `quadratic` that solves quadratic equations and prints their roots. Recall that a quadratic equation is a polynomial equation in terms of a variable x of the form a x2 + b x + c = 0. The formula for solving a quadratic equation is:

Here are some example equations and their roots:

equation call x2 - 7x + 12 x2 + 3x + 2 `quadratic(1, -7, 12);` `quadratic(1, 3, 2);` ```First root = 4.0 Second root = 3.0 ``` ```First root = -1.0 Second root = -2.0 ```

But for some values of a, b, and c, the formula does not find any valid roots. Under what conditions would this formula fail? Modify the `quadratic` method so that it will reject invalid values of a, b, or c by throwing an `IllegalArgumentException`. (You may want to go back and complete the exercise in the previous chapter first.)

Type your solution here:

This is a method problem. Write a Java method as described. Do not write a complete program or class; just the method(s) above.

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