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 the equation that has exactly the same solutions as \((x - 7)(x + 9) = 0\), we first solve for the values of \(x\) that satisfy this equation.

Setting each factor equal to zero:

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

So the solutions to the equation \((x - 7)(x + 9) = 0\) are \(x = 7\) and \(x = -9\).

Now we will check each option to see if it produces the same solutions.

A. \(x^2 - 2x - 63 = 0\)
To find the solutions, we can factor this or use the quadratic formula. Factoring, we look for two numbers that multiply to \(-63\) and add to \(-2\). The factors are \(7\) and \(-9\): \[ (x - 9)(x + 7) = 0 \] Setting each factor to zero:

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

This does not match our solutions.

B. \(x^2 + 2x = -63\)
Rearranging gives: \[ x^2 + 2x + 63 = 0 \] Using the quadratic formula: \[ x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} = \frac{-2 \pm \sqrt{2^2 - 4(1)(63)}}{2(1)} = \frac{-2 \pm \sqrt{4 - 252}}{2} = \frac{-2 \pm \sqrt{-248}}{2} \] Since we have a negative discriminant, this equation has no real solutions.

C. \(x^2 = 2x - 63\)
Rearranging gives: \[ x^2 - 2x + 63 = 0 \] Using the quadratic formula here as well: \[ x = \frac{2 \pm \sqrt{(-2)^2 - 4(1)(63)}}{2(1)} = \frac{2 \pm \sqrt{4 - 252}}{2} = \frac{2 \pm \sqrt{-248}}{2} \] Again, we have a negative discriminant, so no real solutions.

D. \(x^2 = -2x + 63\)
Rearranging gives: \[ x^2 + 2x - 63 = 0 \] Factoring this: \[ (x + 9)(x - 7) = 0 \] Setting the factors to zero:

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

This matches the solutions from the original equation.

Hence, the correct answer is D. \(x^2 = -2x + 63\).