JAMB 2001 · UME · Q27

Find the locus of a point which moves such that its distance from the line $y = 4$ is a constant $k$ .

Worked solution (try it first)

$y = 4$ is a horizontal line.
Points a distance $k$ from it lie on two horizontal lines, one above and one below.
The line above is $y = 4 + k$ and the line below is $y = 4 - k$ .
So the locus is $y = 4 \pm k$ , option D.