Question

Given the function f(x) = x2 and k = 2, which of the following represents a horizontal shift?

Answer 1

A horizontal shift would be in the form f(x±k)

Answer 2

Solutions 

To solve problems like that we have to use the rules 

f(x)+k = vertical shift
kf(x) = vertical stretch/shrink (depending)
f(x+k) = phase shift, also known as a horizantal shift.
f(kx) = Horizantal stretch/shrink

The  horizontal shift would be in the form f(x±k)