What is the slope of a line that is perpendicular to the line y = 1?

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.