y = 1
Using y = mx + c.
Compare to y = 1, y = 0x + 1 ,
We can see that the slope m = 0 and the vertical intercept, c = 1.
For the line perpendicular to y = 1
Condition for perpendicularity m₁m₂ = -1
m₁ = 0, m₂ = ?
0*m₂ = -1
m₂ = -1/0 = Negative Infinite or Infinite
Slope of line perpendicular to y = 1, is = Infinite.