Why does a horizontal line have a slope of zero, but a vertical line have an undefined slope?

Refer to the diagram shown below.
Define two positions on each line as A (x₁, y₁) and B(x₂, y₂).
Then the slope is


Horizontal line:
Define A (0, 1) and B (1,1).
The slope is


Vertical line:
Define A( (1,0) and B(1,1).
The slope is
  (undefined)

Answercounterclockwise rotation about the origin by 180 degrees followed by reflection about the y-axisexplanationthe given figure has verticesrecall that for counterclockwise rotation about the origin, when we rotate figure pqrs counterclockwise through an angle of 180° about the origin, the coordinates will becomenext, we reflect in the y-axis by negating the x-coordinates of the resulting figure to obtain,therefore the correct answer is c