Example Solve 3x² - 2 x -11 = 0.

Solution

In this case the polynomial doesn't factor thus we can't do that step.  Though, still we do have to know where the polynomial is zero. We ought to use the quadratic formula for that.  Here is what the quadratic formula gives us.

                                                        x = (1 ± √ 34)/3

In order to work the problem we'll have to reduce this to decimals.

x = (1 +√34)/3 = 2.27698                                         x = (1 -√34) /3 = -1.61032

From this instance on the procedure is identical to the earlier examples. In the number line below the dashed lines are at the estimated values of the two decimals above & the inequalities illustrate the value of the quadratic evaluated at the test points illustrated.

Thus, it looks like we required the two outer regions for the solution.  Here is the inequality & interval notation for the solution.

-∞ < x < (1 - √34 )/3                            and          ( 1 +  √34 )/3

-∞, (1- √ 34) /3                                         and  ( 1 +√34 /3, , ∞ )