ACT Mathematics Practice Test

When a parabola is written as y = ax^2 + bx + c, its vertex occurs at the x-coordinate x = -b/(2a). Here a = 1 and b = -4, so x = -(-4)/(2·1) = 2. To find the y-coordinate, substitute x = 2: y = 2^2 - 4(2) + 5 = 4 - 8 + 5 = 1. So the vertex is (2, 1). Another way to see this is by completing the square: y = (x - 2)^2 + 1, which makes the vertex obvious at (2, 1). The other points listed don’t match the vertex coordinates.