Perpendicular Lines

Definition

Perpendicular lines are a pair of lines that intersect at right angles, forming a 90-degree angle. This geometric relationship is an important concept in understanding the slope of a line.

5 Must Know Facts For Your Next Test

1. The slope of a line that is perpendicular to another line is the negative reciprocal of the original line's slope.
2. When two lines are perpendicular, the product of their slopes is -1.
3. Perpendicular lines can be used to divide a plane into four equal quadrants.
4. The angle formed by two perpendicular lines is always 90 degrees.
5. Perpendicular lines are often used in construction, engineering, and design to create stable, balanced structures.

Review Questions

• Explain how the slope of a line is related to the concept of perpendicular lines.
  • The slope of a line that is perpendicular to another line is the negative reciprocal of the original line's slope. This means that if the slope of one line is $m$, the slope of the perpendicular line will be $-1/m$. This relationship is important because it allows you to determine the slope of a perpendicular line given the slope of the original line, or vice versa. Understanding this connection between slope and perpendicular lines is crucial for solving problems involving the properties of lines.
• Describe how perpendicular lines can be used to divide a plane into four equal quadrants.
  • When two perpendicular lines intersect, they create four equal angles, each measuring 90 degrees. These four angles divide the plane into four equal quadrants. This property of perpendicular lines is useful in various applications, such as in coordinate geometry, where the $x$-axis and $y$-axis form perpendicular lines that divide the coordinate plane into four quadrants. Understanding how perpendicular lines create this quadrant structure can help you visualize and analyze the relationships between points, lines, and shapes in the coordinate plane.
• Analyze the significance of the 90-degree angle formed by perpendicular lines and explain how this relates to the concept of slope.
  • The 90-degree angle formed by perpendicular lines is a crucial aspect of their definition and has important implications for understanding slope. The 90-degree angle means that the slopes of the two perpendicular lines have a specific relationship: the product of their slopes is -1. This relationship arises from the fact that the tangent of a 90-degree angle is undefined, as the vertical change is infinite compared to the horizontal change. Recognizing and applying this property of perpendicular lines is essential for solving problems involving the slope of lines, as it allows you to determine the slope of one line given the slope of the other.

Related terms

Slope: The slope of a line is a measure of the steepness of the line, typically expressed as the ratio of the vertical change to the horizontal change between two points on the line.

Angle: An angle is the measure of the space between two intersecting lines or between two portions of the same line.

Parallel Lines: Parallel lines are a pair of lines that are equidistant from each other and never intersect.