Each of the following quadratic equations can be solved by factoring. Which equation has only one distinct solution?
A. x^2 + 4x + 4 = 0
B. x^2 - 4 = 0
C. x^2 - 5x + 4 = 0
D. x^2 + 5x + 4 = 0
A. x^2 + 4x + 4 = 0 can be factored into (x + 2)(x + 2) = 0, which has one distinct solution x = -2.
B. x^2 - 4 = 0 can be factored into (x - 2)(x + 2) = 0, which has two distinct solutions x = -2 and x = 2.
C. x^2 - 5x + 4 = 0 can be factored into (x - 4)(x - 1) = 0, which has two distinct solutions x = 4 and x = 1.
D. x^2 + 5x + 4 = 0 can be factored into (x + 1)(x + 4) = 0, which has two distinct solutions x = -1 and x = -4.
Therefore, the only quadratic equation with only one distinct solution is A. x^2 + 4x + 4 = 0.