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

A. x^2=2x-63
B. x^2=-2x+63
C. x^2+2x=-63
D. x^2-2x-63=0

1 answer

To determine which of the given equations has the same solution as \((x-7)(x+9)=0\), we first need to solve the original equation.

The solutions to \((x-7)(x+9)=0\) can be found by setting each factor equal to zero:

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

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

Next, we will check each of the options to see if they also yield these same solutions.

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

Rearranging gives: \[ x^2 - 2x + 63 = 0 \] Using the quadratic formula to find the solutions: \[ x = \frac{-(-2) \pm \sqrt{(-2)^2 - 4 \cdot 1 \cdot 63}}{2 \cdot 1} = \frac{2 \pm \sqrt{4 - 252}}{2} = \frac{2 \pm \sqrt{-248}}{2} \] Since the discriminant is negative, this does not have real solutions.

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

Rearranging gives: \[ x^2 + 2x - 63 = 0 \] Using the quadratic formula: \[ x = \frac{-2 \pm \sqrt{(2)^2 - 4 \cdot 1 \cdot (-63)}}{2 \cdot 1} = \frac{-2 \pm \sqrt{4 + 252}}{2} = \frac{-2 \pm \sqrt{256}}{2} = \frac{-2 \pm 16}{2} \] Calculating:

  1. \(x = \frac{14}{2} = 7\)
  2. \(x = \frac{-18}{2} = -9\)

This option has the same solutions \(x = 7\) and \(x = -9\).

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

Rearranging gives: \[ x^2 + 2x + 63 = 0 \] Using the quadratic formula: \[ x = \frac{-2 \pm \sqrt{(2)^2 - 4 \cdot 1 \cdot 63}}{2 \cdot 1} = \frac{-2 \pm \sqrt{4 - 252}}{2} = \frac{-2 \pm \sqrt{-248}}{2} \] This again yields no real solutions.

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

Using the quadratic formula: \[ x = \frac{2 \pm \sqrt{(-2)^2 - 4 \cdot 1 \cdot (-63)}}{2 \cdot 1} = \frac{2 \pm \sqrt{4 + 252}}{2} = \frac{2 \pm \sqrt{256}}{2} = \frac{2 \pm 16}{2} \] Calculating:

  1. \(x = \frac{18}{2} = 9\)
  2. \(x = \frac{-14}{2} = -7\)

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

In conclusion, the equation that has exactly the same solutions as \((x-7)(x+9)=0\) is option B: \(x^2 = -2x + 63\).