An equation has only one distinct solution when it can be factored into a perfect square. This happens when the discriminant (b² - 4ac) equals zero.
Let's analyze each equation:
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\(x^2 + 4x + 4 = 0\):
- This factors to \((x + 2)^2 = 0\).
- It has one distinct solution: \(x = -2\).
-
\(x^2 + 5x + 4 = 0\):
- This factors to \((x + 4)(x + 1) = 0\).
- It has two distinct solutions: \(x = -4\) and \(x = -1\).
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\(x^2 - 5x + 4 = 0\):
- This factors to \((x - 4)(x - 1) = 0\).
- It has two distinct solutions: \(x = 4\) and \(x = 1\).
-
\(x^2 - 4 = 0\):
- This factors to \((x - 2)(x + 2) = 0\).
- It has two distinct solutions: \(x = 2\) and \(x = -2\).
Therefore, the equation that has only one distinct solution is:
\(x^2 + 4x + 4 = 0\).