Help with Quadratic Equations by completing the square

In summary: To do this I would first take the coefficient of the linear term which is -14, divide by 2 to get -7, then square to get 49. Then I would add 49 to both sides to complete the square. This gives us the following:x2 - 14x + 49 = 49Finally we can factor the left hand side to get (x - 7)^2 = 49. Taking the square root of both sides we get x - 7 = ±7. Solving for x we get x = 7 ± 7, which simplifies to x = 14 or x = 0.In summary, when solving equations where the square is on the other side of the equal
  • #1
Maddsnicole
1
0
I understand how to solve these equations when the square is on this side of the equal sign: x2 + 8x + 7 = 27

But when the square is on the other side, I am thrown. Like this one...
x2 = 14x - 33

The solutions manual shows the next step as the following, but what do you do to get to this point?
x2 - 14x + 49 = -33 + 49
 
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  • #2
We are given:

\(\displaystyle x^2=14x-33\)

Subtract through by $14x$:

\(\displaystyle x^2-14x=-33\)

Take the coefficient of the linear term which is -14, divide by 2 to get -7, then square to get 49, and so add 49 to both sides:

\(\displaystyle x^2-14x+49=-33+49\)

Does this make sense?
 
  • #3
Maddsnicole said:
I understand how to solve these equations when the square is on this side of the equal sign: x2 + 8x + 7 = 27

But when the square is on the other side, I am thrown. Like this one...
x2 = 14x - 33

The solutions manual shows the next step as the following, but what do you do to get to this point?
x2 - 14x + 49 = -33 + 49

I would not have followed the solution manuals next step. From the question

x2 = 14x - 33

I would first move everything over to the left hand side (because this is where the x2 is).

When you do this the terms you move from one side to the other need to change signs (positive becomes negative, negative becomes positive) so you should get this:

x2 - 14x + 33 = 0

From here I would complete the square as normal.
 

FAQ: Help with Quadratic Equations by completing the square

What is completing the square in quadratic equations?

Completing the square is a method used to solve quadratic equations by adding a constant term to both sides of the equation in order to create a perfect square trinomial.

Why is completing the square useful?

Completing the square is useful because it allows us to solve quadratic equations that cannot be easily solved by factoring or using the quadratic formula. It also helps us find the vertex of a parabola, which is useful in applications such as optimization problems.

Can I use completing the square for any quadratic equation?

Yes, completing the square can be used for any quadratic equation in the form ax^2 + bx + c = 0, where a, b, and c are real numbers.

How do I complete the square in a quadratic equation?

To complete the square, follow these steps:
1. Move the constant term to the right side of the equation
2. Divide the coefficient of the x^2 term by 2 and square it
3. Add the squared term to both sides of the equation
4. Factor the perfect square trinomial on the left side of the equation
5. Take the square root of both sides to solve for x.

Can completing the square give me complex solutions?

Yes, completing the square can give you complex solutions if the discriminant (b^2 - 4ac) is negative. In this case, the solutions will be in the form of a complex number, a + bi, where a and b are real numbers and i is the imaginary unit.

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