Given the function f (x) = x^2 and k=2, which of the following represents a horizontal shift?

F (x) + k, kf (x), f (x+k), f (kx)

F (x) = x²

k = 2

f (x) + k = x² + 2

kf (x) = 2x²

f (x + k) = (x + 2) ²

f (x + k) = (x + 2) (x + 2)

f (x + k) = x (x + 2) + 2 (x + 2)

f (x + k) = x (x) + x (2) + 2 (x) + 2 (2)

f (x + k) = x² + 2x + 2x + 4

f (x + k) = x² + 4x + 4

f (kx) = (2x) ²

f (kx) = 4x²

The answers are f (x) + k and f (x + k).