9) If a horizontal line passes through an ordered pair \( (a, b) \), what is the equation of the line? a) \( y=b \) b) \( x=b \) c) \( 0 y=a \) d) \( 0 x=a \)

The equation of a horizontal line passing through the point \( (a, b) \) remains constant in the \( y \)-direction, which means it doesn’t change as \( x \) varies. Thus, it keeps the value of \( y \) equal to \( b \) at all points along the line. Therefore, the correct choice is \( a) \, y=b \). Horizontal lines are not only mathematically significant but can also be physically observed—think of calm oceans under a horizon or flat plains. Just like in math, these natural formations maintain a steady height, making our exploration of the outdoors a wonderful real-world example of mathematical concepts!