One of the five quadratics below has a repeated root. (The other four have distinct roots.) What is the repeated root?

x^2 - 2x + 1

x^2 - 4x - 4

x^2 + 6x - 9

x^2 + 26x + 25

x^2 - 5x + 4

x^{2} – 2x + 1 has a repeated root. Factor to (x – 1)(x – 1)

or another way of saying that is (x – 1)^{2} and the root is 1.

edited to add: The root is 1 if x^{2} – 2x + 1 equals zero.

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