From the equations which represents the following Pair of lines
y - 3x = 0 , y + 3x = 0

Explanation

y - 3x = 0 , y + 3x = 0
`therefore` (y-3x)(y+3x) = 0
or, `y^2 - 9x^2 = 0 `
which is the equation of a pair of lines.