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Which equation has the solutions x = 1 plus-or-minus √5?

1) x² + 2x + 4 = 0
2) x² - 2x + 4 = 0
3) x² + 2x - 4 = 0
4) x² - 2x - 4 = 0

1 Answer

7 votes

Final answer:

The correct equation with solutions x = 1 ± √5 is x^2 - 2x - 4 = 0. By matching the given solutions to the form of the quadratic formula, it's determined that option 4 fits the required coefficients to produce the desired roots.

Step-by-step explanation:

The student is asking which equation has the solutions x = 1 ± √5. To identify the correct equation, we need to consider the fact that the solutions provided are in the form that would result from using the quadratic formula, which is typically x = √{-b ± √{b^2-4ac}}/2a for a quadratic equation ax^2+bx+c = 0.

Since the solutions are x = 1 ± √5, this implies that:

  • The coefficient of x (the b value) must be the opposite of twice the constant term (the x-intercept), so b = -2(1) = -2.
  • The constant term (the c value) when substituted into the quadratic formula equation √{b^2-4ac} should give ±√5 after simplification.

The only equation that fits this description is x^2 - 2x - 4 = 0. Checking:

  • b^2-4ac becomes (-2)^2 - 4(1)(-4) which simplifies to 4 + 16, resulting in √20.
  • Since √20 is the same as 2√5 and the quadratic formula divides this value by 2a (with a being 1 in this case), it reduces back to ±√5.

Therefore, the correct equation is x^2 - 2x - 4 = 0, which is option 4.

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