The slope formula is used to calculate the inclination or steepness of a line. It finds application in determining the slope of any line by finding the ratio of the change in the y-axis to the change in the x-axis. The slope of a line is defined as the change in the "y" coordinate with respect to the change in the "x" coordinate of that line.
What is the Slope Formula?
The slope formula refers to the formula used to calculate the steepness of a line and determines how much it's inclined. To calculate the slope of the lines, the x and y coordinates of the points lying on the line can be used. In other words, it is the ratio of the change in the y-axis to the change in the x-axis.
Slope Formula
The formula to calculate slope is given as,
m = (y2 - y1)/(x2 - x1) = Δy/Δx
where, m is the slope of the line,x1, x2 are the coordinates of the x-axis, and y1, y2 are the coordinates of the y-axis.
Derivation of Slope Formula
The x and y coordinates of the line are used to calculate the slope of the line. The net change in y coordinate is Δy, while the net change in the x coordinate is Δx. So the change in y coordinate with respect to the change in x coordinate can be written as,
m = Δy/Δx
where
- m is the slope
- Δy is the change in y-coordinates
- Δx is the change in the x-coordinates
We know that tan θ is also the slope of the line where θ is the angle made by the line with the positive direction of the x-axis.
And, tanθ = height/base
Since the height/base between any two given points = (y2 - y1)/(x2 - x1)
Thus, the slope equation is, m = tanθ = Δy/Δx
From the graph, we observe:
- Δy = (y2 - y1)
- Δx = (x2 - x1)
Thus, the slope formula is given as: Slope = m = (y2 - y1)/(x2 - x1)
Slope Equation
As we discussed in the previous section, the slope formula can be used to determine the slope of any line. The equation that can be used in finding this slope can therefore written as,
m = rise/run = tanθ = Δy/Δx = (y2 - y1)/(x2 - x1)
where,
- m is the slope
- Δy is the change in y-coordinates
- Δx is the change in the x-coordinates
- θ is the angle made by the line with the positive x-axis
Also, the equation of slope of any line using the line equation can be given as,
y = mx + b
where,
- m is the slope of the line
- b is the y-intercept of the line
Let us see the applications of the slope formula in the following solved examples.
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Examples Using Slope Formula
Example 1: Find the slope of a line whose coordinates are (2,9) and (4,1)?
Solution:
To find: The slope of the line with coordinates (2,9) and (4,1)
Given, (x1, y1) = (2, 9) and (x2, y2) = (4, 1)
The slope formula is m = (y2 - y1)/(x2 - x1)
m = (1 − 9)/(4 − 2)
m = -8/2 = -4
Answer: Slope of the given line = -4
Example 2: Determine the value of b, if the slope of a line passing through the points (b, 7) and (8, -5) is 6.
Solution:
To find: the value of b
Given, Slope = m = 6, Points: (x1, y1) = (b, 7) and (x2, y2) = (8, -5)
We know that Slope (m) = (y2 - y1)/(x2 - x1)
6 = (-5-7)/(8-b)
6 = (-12)/(8-b)
-2= (8-b)
-2-8 = -b,
b = 10
Answer: The value of b = 10.
Example 3: If the angle made by a line with the positive y−axis is 30°, then what is the value of the slope of the line?
Solution:
To find: slope of the line
Given: Angle made by a line with the positive y−axis = 30°
We know that if the line makes an angle of 30° from the positive y-axis, then it makes an angle of 120° from the positive x-axis. Therefore, the value of the slope of the line is tan120° = -√3
Answer: The value of the slope of the line = -√3
FAQs on Slope Formula
What is the Slope Formula in Geometry?
In geometry, the slope formula is defined as the formula to calculate the slope of any line by finding the ratio of the change in the y-axis to the change in the x-axis.
What does m Stand For in Slope Formula?
In the slope formula, m stands for slope which is calculated as the m = (y2 - y1)/(x2 - x1) = Δy/Δx
What is the Slope Formula Used For?
The slope formula is used to calculate the steepness of a line and the x and y coordinates of the lines are used for the same. We know that the slope of a line is one of the most important characteristics of a line as it helps to measure the rate of change.
How to Calculate Slope Using Slope Formula?
The slope of a line can be calculated using the following formulas:
When coordinates are given:
- Step 1: Find the coordinates of the line.
- Step 2: Put their values in the formula, (m) = (y2 - y1)/(x2 - x1)
When angle is given:
- Step 1: Identify the angle made with the axis.
- Step 2: Put the value in the formula, m = tanθ
What is the Equation of Slope of a Line?
The equation of slope of any line can be calculated using the following formula,
m = rise/run = tanθ = Δy/Δx = (y2 - y1)/(x2 - x1)
where,
- m is the slope
- Δy is the change in y-coordinates
- Δx is the change in the x-coordinates
- θ is the angle made by the line with the positive x-axis
The slope equation using the equation of line is given as, y = mx + b, here, m is the slope and b is the y-intercept.
