y = x^2 - 4x + 4
y' = 2x - 4
Setting y' to zero, we have:
2x - 4 = 0
2x = 4
x = 4 / 2
x = 2
When x < 2, y' < 0. This means y is decreasing for x < 2.
When x > 2, y' > 0. This means y is increasing for x > 2.
Hence, by 1st derivative test, y has a relative minimum at x = 2.