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JEE Main 2026 Preparation: Question Papers, Solutions, Mock Tests & Strategy Unacademy » JEE Study Material » Mathematics » Properties and Relation of Straight Lines

Properties and Relation of Straight Lines

A line is a collection of points that only has length and not breath or thickness.

Table of Content
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Properties Straight Line

Straight lines have the following qualities.

  • The length of a straight line is endless. We will never be able to calculate the distance between the line’s two extreme points
  • There are no areas and no volume in a straight line. However, it has an infinite length
  • A one-dimensional figure is a straight line
  • A single point can have an endless number of lines passing through it, but only one line travels through two points.

Equation of a Straight Line

A linear equation is a straight line equation. Based on known variables, angles, and constants, a straight line on a cartesian plane can have various representations. The slope of a straight line dictates the line’s direction and indicates how steep it is. Rise over run is calculated as the difference in y coordinates divided by the difference in x coordinates. A straight line equation can take many different forms. These are the details:

Straight Line Equation in General

A straight line’s general equation can be written as

ax + by + c = 0, where

  • x and y are variables, while a, b, and c are constants.
  • -a/b is the slope.

Y-intercept and Slope Form

A straight line with slope m = tanθ and y-intercept b is given by: y = mx + b, where m is the slope and θ is the angle formed by the line with the positive x-axis.

xl1

Slope Point form

A straight line passing through a point (x1, y1) with slope m =tanθ, where is the θ angle formed by the line with the positive x-axis, is given by: y – y1 = m(x – x1)

xl2

Two Points Form

In the two-point form, a straight line passing between points (x1, y1) and (x2, y2) is represented by: y – y1 = [(y2 – y1) / (x2 – x1)] (x – x1).

xl3

Intercept Form

The intercept form of a straight line with x-intercept a and y-intercept b, as illustrated in the diagram below, where point A is on the x-axis (vertical here) and point B is on the y-axis (horizontal here), is x/a + y/b = 1.

xl4

Lines Parallel to the X-axis or Y-axis Equation

y = ±a, where an is the equation of a line parallel to the x-axis.

  • a is the line’s distance from the x-axis. If an is above the x-axis, it has a positive value, and if it is below the x-axis, it has a negative value.

x =±b, where b is the equation of a line parallel to the y-axis.

  • The distance between the line and the y-axis is b. If b is on the right side of the y-axis, it has a positive value, and if it is on the left side, it has a negative value.

The figure below shows lines parallel to the x- and y-axes, respectively.

xl5

Slopes of Various Types

The slope of a line is the angle created by a line with a positive x-axis. With the x-axis, different lines form different angles. A line can have slopes that are positive, negative, zero, or infinite. Let’s look at a few examples.

Slope of 0

The slope of a line that creates a 0° angle with the x-axis is 0. m = tanθ is the formula for calculating the slope of a line.

Here, θ = 0° . As a result, m = tan0 = 0. As a result, a line with a slope of 0 is perpendicular to the x-axis.

xl6

Slope: Positive

The slope of a line is positive if it produces an angle with the x-axis between 0 and 90 degrees.

xl7

Slope is Negative

The slope of a line is negative when it makes an angle with the x-axis between 90° and 180°.

xl8

Slope Without End

The slope of a line that forms a 90° angle with the x-axis or is parallel to the y-axis is neither specified nor infinite.

The slope of a line is defined as m = tanθ.

Here, θ = 90° . The slope m = tan 90° is unknown. As a result, the infinitely sloped line is parallel to the y-axis.

xl9

Important Points to Remember About Straight Lines

Here is a list of some important points to consider when studying straight lines:

  • Three non-collinear points cannot be crossed by a straight line.

  • When two lines l and m intersect, the relationship l = k x m holds, where k is a real number.

  • tanθ =(m2 – m1)/(1 + m2 m1) can be used to compute the acute angle between two lines with slopes m1 and m2, where m2 > m1.

Conclusion

The length of a straight line is endless. We will never be able to calculate the distance between the line’s two extreme points.There are no areas and no volume in a straight line. However, it has an infinite length.A one-dimensional figure is a straight line.A single point can have an endless number of lines passing through it, but only one line travels through two points.A linear equation is a straight line equation. Based on known variables, angles, and constants, a straight line on a cartesian plane can have various representations. The slope of a straight line dictates the line’s direction and indicates how steep it is.A straight line with slope m = tanθ and y-intercept b is given by: y = mx + b, where m is the slope and θ is the angle formed by the line with the positive x-axis.Three non-collinear points cannot be crossed by a straight line.

faq

Frequently asked questions

Get answers to the most common queries related to the JEE Examination Preparation.

What Do Parallel Straight Lines Mean?

Ans. If two lines are in the same plane but never meet, they are said to be p...Read full

To Draw a Straight Line, What Do You Use?

Ans. A ruler, t-squares, or other tools can be used to draw a straight line. To draw a straight line between two poi...Read full

What is the straight line condition?

Ans. A line is just a geometric entity with zero width that extends on both sides. A straight line is one that has n...Read full

What is the straight line equation?

Ans. A straight line’s general equation is y = m x + c, where m is the slope and c is the y-intercept....Read full

What is the angle formed by two perpendicular straight lines?

Ans. The two perpendicular lines meet at a 90-degree angle. The slopes of the two perpendicular lines are lined in s...Read full

Ans. If two lines are in the same plane but never meet, they are said to be parallel lines. The angle between parallel lines is either 0 degrees or 180 degrees. They are pointing in the same direction as one another. If we have two parallel lines and know the slope of one, we may equate the slope of the second line to the slope of the first and get the slope of the other line.

Ans. A ruler, t-squares, or other tools can be used to draw a straight line. To draw a straight line between two points, many geometric tools with a smooth and flat surface can be employed. A line segment is a straight line that is drawn between two points. Rulers are the most common instrument for drawing a straight line between two points or in general.

Ans. A line is just a geometric entity with zero width that extends on both sides. A straight line is one that has no bends. A straight line is a line that stretches to infinity on both sides and has no bends.

Ans. A straight line’s general equation is y = m x + c, where m is the slope and c is the y-intercept.

Ans. The two perpendicular lines meet at a 90-degree angle. The slopes of the two perpendicular lines are lined in such a way that the product of their slopes equals -1. Perpendicular lines can be found in many places, such as the corners of tables and rooms, and we can measure the angle between the sides to determine that the angle between the perpendicular lines is 90 degrees.

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