A quadratic equation has only one distinct solution when its discriminant (b² - 4ac) is equal to zero.
Let's analyze the provided equations:
-
x² − 5x + 4 = 0
- a = 1, b = -5, c = 4
- Discriminant: (-5)² - 4(1)(4) = 25 - 16 = 9 (two distinct solutions)
-
x² + 5x + 4 = 0
- a = 1, b = 5, c = 4
- Discriminant: (5)² - 4(1)(4) = 25 - 16 = 9 (two distinct solutions)
-
x² + 4x + 4 = 0
- a = 1, b = 4, c = 4
- Discriminant: (4)² - 4(1)(4) = 16 - 16 = 0 (one distinct solution)
-
x² − 4 = 0
- a = 1, b = 0, c = -4
- Discriminant: (0)² - 4(1)(-4) = 0 + 16 = 16 (two distinct solutions)
The equation that has only one distinct solution is:
x² + 4x + 4 = 0.