Forgetting to Move the Constant Term

Oct 13, 2025 by wbrum.org 111 views

Introduction

Completing the square is a powerful algebraic technique used to solve quadratic equations. It involves manipulating the equation to express it in a perfect square trinomial form, which can be easily solved. In this article, we will focus on solving the quadratic equation ${ r^2 - 28r = -3 }$ by completing the square.

What is Completing the Square?

Completing the square is a method of solving quadratic equations of the form ${ ax^2 + bx + c = 0 }$ . The goal is to rewrite the equation in the form ${ a(x - h)^2 + k = 0 }$ , where ${ (h, k) }$ is the vertex of the parabola represented by the equation. This form is useful because it allows us to easily identify the x-intercepts of the parabola, which are the solutions to the equation.

Step 1: Move the Constant Term to the Right Side

To complete the square, we need to move the constant term to the right side of the equation. This gives us:

${ r^2 - 28r + 3 = 0 }$

Step 2: Find the Value to Add

To complete the square, we need to find a value to add to both sides of the equation. This value is half of the coefficient of the linear term squared. In this case, the coefficient of the linear term is -28, so we need to find half of -28 squared.

${ \text{Value to add} = \left( \frac{-28}{2} \right)^2 = (-14)^2 = 196 }$

Step 3: Add the Value to Both Sides

Now that we have found the value to add, we can add it to both sides of the equation.

${ r^2 - 28r + 196 = 3 + 196 }$

Step 4: Simplify the Equation

Simplifying the equation, we get:

${ (r - 14)^2 = 199 }$

Step 5: Take the Square Root

Taking the square root of both sides of the equation, we get:

${ r - 14 = \pm \sqrt{199} }$

Step 6: Solve for r

Solving for r, we get:

${ r = 14 \pm \sqrt{199} }$

Rounding the Answer

Rounding the answer to the nearest hundredth, we get:

${ r = 14 \pm 14.13 }$

Conclusion

In this article, we have solved the quadratic equation ${ r^2 - 28r = -3 }$ by completing the square. We have followed the steps of moving the constant term to the right side, finding the value to add, adding the value to both sides, simplifying the equation, taking the square root, and solving for r. The final answer is ${ r = 14 \pm 14.13 }$ .

Example Use Case

Completing the square is a useful technique in many real-world applications, such as:

Physics: To solve problems involving motion under constant acceleration.
Engineering: To design and optimize systems, such as bridges and buildings.
Computer Science: To solve problems involving quadratic equations in computer graphics and game development.

Tips and Variations

Use the Quadratic Formula: If the equation is not easily solvable by completing the square, you can use the quadratic formula to find the solutions.
Use a Calculator: If you are not comfortable with the calculations, you can use a calculator to find the solutions.
Check Your Work: Always check your work by plugging the solutions back into the original equation to ensure that they are true.

Common Mistakes

Forgetting to Move the Constant Term: Make sure to move the constant term to the right side of the equation.
Forgetting to Add the Value: Make sure to add the value to both sides of the equation.
Not Simplifying the Equation: Make sure to simplify the equation after adding the value.

Conclusion

Q: What is completing the square?

A: Completing the square is a method of solving quadratic equations of the form ${ ax^2 + bx + c = 0 }$ by rewriting the equation in the form ${ a(x - h)^2 + k = 0 }$ , where ${ (h, k) }$ is the vertex of the parabola represented by the equation.

Q: How do I know when to use completing the square?

A: You should use completing the square when the quadratic equation is not easily solvable by factoring or using the quadratic formula. Completing the square is particularly useful when the equation has a coefficient of 1 on the ${ x^2 }$ term.

Q: What are the steps to complete the square?

A: The steps to complete the square are:

Move the constant term to the right side of the equation.
Find the value to add by taking half of the coefficient of the linear term squared.
Add the value to both sides of the equation.
Simplify the equation.
Take the square root of both sides of the equation.
Solve for x.

Q: What is the value to add?

A: The value to add is half of the coefficient of the linear term squared. For example, if the coefficient of the linear term is -28, the value to add is ${ \left( \frac{-28}{2} \right)^2 = (-14)^2 = 196 }$ .

Q: Why do I need to add the value to both sides of the equation?

A: You need to add the value to both sides of the equation to maintain the equality of the equation. This ensures that the equation remains true after adding the value.

Q: Can I use completing the square with any type of quadratic equation?

A: Yes, you can use completing the square with any type of quadratic equation, including those with complex coefficients or those that are not easily solvable by factoring or using the quadratic formula.

Q: What are some common mistakes to avoid when completing the square?

A: Some common mistakes to avoid when completing the square include:

Forgetting to move the constant term to the right side of the equation.
Forgetting to add the value to both sides of the equation.
Not simplifying the equation after adding the value.

Q: Can I use a calculator to complete the square?

A: Yes, you can use a calculator to complete the square. However, it's always a good idea to check your work by plugging the solutions back into the original equation to ensure that they are true.

Q: How do I check my work when completing the square?

A: To check your work, plug the solutions back into the original equation to ensure that they are true. You can also use a calculator to check your work.

Q: What are some real-world applications of completing the square?

A: Completing the square has many real-world applications, including:

Physics: To solve problems involving motion under constant acceleration.
Engineering: To design and optimize systems, such as bridges and buildings.
Computer Science: To solve problems involving quadratic equations in computer graphics and game development.

Q: Can I use completing the square to solve systems of equations?

A: Yes, you can use completing the square to solve systems of equations. However, it's often more efficient to use other methods, such as substitution or elimination, to solve systems of equations.

Q: What are some tips for mastering completing the square?

A: Some tips for mastering completing the square include:

Practice, practice, practice: The more you practice completing the square, the more comfortable you will become with the process.
Use a calculator: A calculator can be a big help when completing the square, especially when dealing with complex equations.
Check your work: Always check your work by plugging the solutions back into the original equation to ensure that they are true.

Conclusion

In conclusion, completing the square is a powerful algebraic technique used to solve quadratic equations. By following the steps outlined in this article and practicing regularly, you can master completing the square and become proficient in solving quadratic equations. Remember to check your work and use a calculator when necessary.