Which of the following equations has exactly the same solutions as (x-7) (x+9) = 0?

A: x^2 - 2x - 63 = 0

B: x^2 + 2x = -63

C: x^2 = 2x - 63

D: x^2 = -2x + 63

1 answer

To find which equation has exactly the same solutions as \((x - 7)(x + 9) = 0\), we first determine the solutions of the given equation.

The equation \((x - 7)(x + 9) = 0\) has solutions when:

  1. \(x - 7 = 0 \implies x = 7\)
  2. \(x + 9 = 0 \implies x = -9\)

Thus, the solutions are \(x = 7\) and \(x = -9\).

Now, let's check each option to see if any produces the same solutions.

Option A: \(x^2 - 2x - 63 = 0\)

To find the roots, we can use the quadratic formula, \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\), where \(a = 1\), \(b = -2\), and \(c = -63\):

\[ x = \frac{-(-2) \pm \sqrt{(-2)^2 - 4 \cdot 1 \cdot (-63)}}{2 \cdot 1} \] \[ = \frac{2 \pm \sqrt{4 + 252}}{2} \] \[ = \frac{2 \pm \sqrt{256}}{2} \] \[ = \frac{2 \pm 16}{2} \]

This gives:

\[ x = \frac{18}{2} = 9 \quad \text{and} \quad x = \frac{-14}{2} = -7 \]

The solutions are \(x = 9\) and \(x = -7\), which do not match.


Option B: \(x^2 + 2x = -63\)

Rearranging gives us:

\[ x^2 + 2x + 63 = 0 \]

Using the quadratic formula with \(a = 1\), \(b = 2\), \(c = 63\):

\[ x = \frac{-2 \pm \sqrt{2^2 - 4 \cdot 1 \cdot 63}}{2 \cdot 1} \] \[ = \frac{-2 \pm \sqrt{4 - 252}}{2} \] \[ = \frac{-2 \pm \sqrt{-248}}{2} \]

This indicates there are complex solutions, which do not match.


Option C: \(x^2 = 2x - 63\)

Rearranging gives us:

\[ x^2 - 2x + 63 = 0 \]

Finding roots:

\[ x = \frac{-(-2) \pm \sqrt{(-2)^2 - 4 \cdot 1 \cdot 63}}{2 \cdot 1} \] \[ = \frac{2 \pm \sqrt{4 - 252}}{2} \] \[ = \frac{2 \pm \sqrt{-248}}{2} \]

Again, this means complex solutions, not matching.


Option D: \(x^2 = -2x + 63\)

Rearranging gives us:

\[ x^2 + 2x - 63 = 0 \]

Using the quadratic formula:

\[ x = \frac{-2 \pm \sqrt{2^2 - 4 \cdot 1 \cdot (-63)}}{2 \cdot 1} \] \[ = \frac{-2 \pm \sqrt{4 + 252}}{2} \] \[ = \frac{-2 \pm \sqrt{256}}{2} \] \[ = \frac{-2 \pm 16}{2} \]

This yields:

\[ x = \frac{14}{2} = 7 \quad \text{and} \quad x = \frac{-18}{2} = -9 \]

Thus, the solutions are \(x = 7\) and \(x = -9\), matching the original equation.

Therefore, the correct answer is:

D: \(x^2 = -2x + 63\).