Algebra II : Completing the Square

Study concepts, example questions & explanations for Algebra II

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Example Questions

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Example Question #1 : Completing The Square

Complete the square in order to find the vertex of this parabola.

Possible Answers:

Correct answer:

Explanation:

To find the vertex of the parabola, you have to get it into vertex form:

The vertex can then be found at the coordinate .

To get to vertex form, we have to complete the square.

Move the 7 over to the other side by subtracting 7 from both sides of the equation:

You're going to have to add something to both sides of the equation...

...the question now is what. What number, when put in the box, would create a "perfect square" on the right-hand side of the equation?

Well, a perfect square trinomial is one whose factors are the same, like so:

In other words, we're looking for .

Well, if is what goes in the box, and is just , then must equal . Now we can solve for .

And since goes in the box, we need to add 4 to both sides:

Now we can factor the right-hand side very neatly:

After we clean up a bit...

...we get:

That gives us a vertex of .

Example Question #2 : Completing The Square

Solve by completing the square:

Possible Answers:

Correct answer:

Explanation:

To complete the square, the equation must be in the form:

 

 

Example Question #223 : Quadratic Equations And Inequalities

Solve the following equation by completing the square. Use a calculator to determine the answer to the closest hundredth.

Possible Answers:

 and 

 and 

No solution

 and 

 and 

Correct answer:

 and 

Explanation:

To solve by completing the square, you should first take the numerical coefficient to the “right side” of the equation:

Then, divide the middle coefficient by 2:

 

Square that and add it to both sides:

 

Now, you can factor the quadratic:

 

 

Take the square root of both sides:

Finish out the solution:

Example Question #3 : Completing The Square

Solve the following equation by completing the square. Use a calculator to determine the answer to the closest hundredth.

Possible Answers:

 and 

 and 

 and 

 and 

 and 

Correct answer:

 and 

Explanation:

To solve by completing the square, you should first take the numerical coefficient to the “right side” of the equation:

 

Then, divide the middle coefficient by 2:

Square that and add it to both sides:

Now, you can easily factor the quadratic:

 

Take the square root of both sides:

 

Finish out the solution:

Example Question #231 : Quadratic Equations And Inequalities

Solve the following equation by completing the square. Use a calculator to determine the answer to the closest hundredth.

Possible Answers:

No solution

 and 

 and 

 and 

 and 

Correct answer:

 and 

Explanation:

To solve by completing the square, you should first take the numerical coefficient to the “right side” of the equation:

Then, divide the middle coefficient by 2:

 

Square that and add it to both sides:

 

Now, you can easily factor the quadratic:

 

Take the square root of both sides:

 

Finish out the solution:

Example Question #3 : Completing The Square

Solve the following equation by completing the square. Use a calculator to determine the answer to the closest hundredth.

Possible Answers:

 and 

 and 

 and 

 and 

No solution

Correct answer:

 and 

Explanation:

To solve by completing the square, you should first take the numerical coefficient to the “right side” of the equation:

 

Then, divide the middle coefficient by 2:

 

Square that and add it to both sides:

 

Now, you can easily factor the quadratic:

 

Take the square root of both sides:

Finish out the solution:

Example Question #232 : Quadratic Equations And Inequalities

Solve the following equation by completing the square. Use a calculator to determine the answer to the closest hundredth.

Possible Answers:

 and 

 and 

No solution

 and 

 and 

Correct answer:

 and 

Explanation:

To solve by completing the square, you should first take the numerical coefficient to the “right side” of the equation:

Then, divide the middle coefficient by 2:

 

Square that and add it to both sides:

Now, you can easily factor the quadratic:

Take the square root of both sides:

Finish out the solution:

Example Question #1531 : Algebra Ii

Solve the following equation by completing the square. Use a calculator to determine the answer to the closest hundredth.

Possible Answers:

 and 

 and 

No solution

 and 

 and 

Correct answer:

No solution

Explanation:

To solve by completing the square, you should first take the numerical coefficient to the “right side” of the equation:

 

Then, divide the middle coefficient by 2:

 

Square that and add it to both sides:

Now, you can easily factor the quadratic:

Your next step would be to take the square root of both sides. At this point, however, you know that you cannot solve the problem. When you take the square root of both sides, you will be forced to take the square root of . This is impossible (at least in terms of real numbers), meaning that this problem must have no real solution.

Example Question #233 : Quadratic Equations And Inequalities

Use completing the square to solve the following equation, simplifying radicals completely:

Possible Answers:

Correct answer:

Explanation:

From the original equation, we add 18 to both sides in order to set up our "completing the square." 

To make completing the square sensible, we divide both sides by 2.

We now divide the x coefficient by 2, square the result, and add that to both sides.

Since the right side is now a perfect square, we can rewrite it as a square binomial.

Take the square root of both sides, simplify the radical and solve for x.

Example Question #234 : Quadratic Equations And Inequalities

Solve the following equation by completing the square:

Possible Answers:

Correct answer:

Explanation:

We start by moving the constant term of the quadratic to the other side of the equation, to set up the "completing the square" format.

Now to make completing the square sensible, we divide boths sides by 2 so that x^2 will not have a coefficient. 

Now we can complete the square by dividing the x coefficient by 2 and squaring the result, then adding that result to both sides.

Because the left side is now a perfect square, we can rewrite it as a squared binomial.

Take the square root of both sides, and then solve for x.

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