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A horizontal line is a straight line that moves from left to right (or right to left) without any vertical movement. The general equation for a horizontal line is expressed as \( y = c \), where \( c \) is a constant value. This equation means that no matter what value the \( x \)-coordinate is, the \( y \)-coordinate remains constant. In our specific example, \( y = -1.5 \) shows that the horizontal line is one and a half units below the x-axis. This characteristic makes it easy to recognize horizontal lines. They are parallel to the x-axis and have a slope of zero, indicating no tilt or steepness. Simple to understand, horizontal lines support many concepts in algebra and geometry. So, remember, a horizontal line like \( y = -1.5 \) stays constant in its height (y-value) and never tilts or slopes.

The y-intercept of a line is the specific point where the line crosses the y-axis. In algebraic terms, it's where \( x = 0 \). To find the y-intercept for any given equation, substitute \( x = 0 \) into the equation and solve for \( y \). For our equation \( y = -1.5 \), it is clear from the start that the line is horizontally placed at \( y = -1.5 \). Thus, the y-intercept directly comes out to be at the point \( (0, -1.5) \). This intercept tells us how high or low the line is along the y-axis. Intercepts are crucial for sketching graphs, as they provide noticeable points where lines cross the axes. Always remember, if the equation of a line is directly given in the form \( y = c \), the y-intercept is instantly \( (0, c) \).

The x-intercept of a line is the point where the line crosses the x-axis. In this case, we look for the point where \( y = 0 \). To determine the x-intercept, we set \( y = 0 \) in the equation and solve for \( x \). For example, consider the horizontal line \( y = -1.5 \). If we set \( y = 0 \), we cannot solve for \( x \) because \( y \) is always \( -1.5 \) and never zero. Therefore, horizontal lines usually do not cross the x-axis unless they are at \( y = 0 \). The absence of an x-intercept in such cases shows how the line runs parallel above or below the x-axis, without an intersection. This concept is useful in understanding graphs and plotting them accurately.