Algebra II : Solving Quadratic Equations

Study concepts, example questions & explanations for Algebra II

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Example Questions

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Example Question #5 : Quadratic Inequalities

Solve:

Possible Answers:

Correct answer:

Explanation:

Start by setting the inequality to zero and by solving for .

Now, plot these two points on to a number line.

1

Notice that these two numbers effectively divide up the number line into three regions:

, and 

Now, choose a number in each of these regions and put it back in the factored inequality to see which cases are true.

For , let 

Since this  is not less than , the solution to this inequality cannot lie in this region.

For , let .

Since this will make the inequality true, the solution can lie in this region.

Finally, for , let 

Since this number is not less than zero, the solution cannot lie in this region.

Thus, the solution to this inequality is 

 

Example Question #7 : Quadratic Inequalities

Solve:

Possible Answers:

The solution cannot be determined with the information given.

Correct answer:

Explanation:

First, set the inequality to zero and solve for .

Now, plot these two numbers on to a number line.

2

Notice how these numbers divide the number line into three regions:

Now, you will choose a number from each of these regions to test to plug back into the inequality to see if the inequality holds true.

For , let 

Since this is not less than zero, the solution to the inequality cannot be found in this region.

For , let 

Since this is less than zero, the solution is found in this region.

For , let 

Since this is not less than zero, the solution is not found in this region.

Then, the solution for this inequality is 

Example Question #6 : Quadratic Inequalities

Solve:

Possible Answers:

Correct answer:

Explanation:

Start by changing the less than sign to an equal sign and solve for .

Now, plot these two numbers on a number line.

4

Notice how the number line is divided into three regions:

Now, choose a number fromeach of these regions to plug back into the inequality to test if the inequality holds.

For , let 

Since this number is not less than zero, the solution cannot be found in this region.

For , let 

Since this number is less than zero, the solution can be found in this region.

For  let .

Since this number is not less than zero, the solution cannot be found in this region.

Because the solution is only negative in the interval , that must be the solution.

 

Example Question #7 : Quadratic Inequalities

Solve:

Possible Answers:

Correct answer:

Explanation:

First, set the inequality to zero and solve for .

 

Now, plot these two numbers on to a number line.

 

3

Notice how these numbers divide the number line into three regions:

Now, you will choose a number from each of these regions to test to plug back into the inequality to see if the inequality holds true.

For , let 

Since this solution is greater than or equal to , the solution can be found in this region.

For , let 

Since this is less than or equal to , the solution cannot be found in this region.

For , let 

Since this is greater than or equal to , the solution can be found in this region.

Because the solution can be found in every single region, the answer to this inequality is 

Example Question #10 : Quadratic Inequalities

Which value for  would satisfy the inequality ?

Possible Answers:

Not enough information to solve

Correct answer:

Explanation:

First, we can factor the quadratic to give us a better understanding of its graph. Factoring gives us: . Now we know that the quadratic has zeros at  and . Furthermore this information reveals that the quadratic is positive. Using this information, we can sketch a graph like this: 

Sketch inequality

We can see that the parabola is below the x-axis (in other words, less than ) between these two zeros  and .

The only x-value satisfying the inequality  is .

The value of  would work if the inequality were inclusive, but since it is strictly less than instead of less than or equal to , that value will not work.

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