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Slope-Intercept Form: Definition & Examples

Slope intercept form

Slope Intercept form is among the four other methods to determine the equation of any straight line. Straight lines are generally represented as y = mx+c. This standard equation of a straight line defines that the x and y variables have a maximum power of unity. This means that x = x1 and y = y1. Also, this confirms that the slope intercept form can be applied only to linear equations. You should be familiar with two-variable linear equations. You should be aware that the graph of such equations is a straight line. You should also be confident about what are the y-intercept, x-intercept, and slope characteristics of linear equations.

If you try to solve an equation like x = 2a3 + y, it might turn a bit tricky, and there’s a probability of getting errors by slope intercept form.    

The other four forms or methods of solving a linear equation are listed below:

  • Slope intercept form
  • Intercept form
  • Two-point form
  • Point slope form

 In this article, you will learn the slope intercept form, what is slope intercept form, slope intercept form equation, how to find slope intercept form, how to write an equation in slope intercept form, and the slope intercept form of a linear equation.

What is Slope Intercept Form?

A straight line’s slope intercept form is amongst the most frequent ways to describe its equation. Consider you are given the slope of a line, and you know that line crosses the y-axis at some point in the cartesian plane. In such cases, it is wise to use the slope intercept form.

You can divide the slope intercept form into two concepts:

  • The slope of a line: The ratio of the difference between the coordinates of the y-axis to the difference between the coordinates of the x-axis.
  • ‘y’ Intercept: The point on the y-axis where the line with a certain slope crosses or intersects is the y-intercept.  

Note: The coordinates of the y-intercept are always (0, y). This is because the line whose equation has to be determined always cuts the y axis at x = 0.

What is the Slope Intercept Form of a Straight Line?

Have a careful look at the figure mentioned below. You will see a straight line ‘AB’ which passes through the 1st quadrant of the coordinate system and cuts the y-axis at point C. The coordinates of this point C are, let’s say, C (0, y). Also, if we see the line ‘ABC’ it inclines some degrees from the x-axis. This is the slope of the given straight line. These are the only things we require to find the equation of a straight line using the slope intercept form. 

Note: If the coordinates of the lines satisfy or agree to the equation, then the coordinates are correct. If the coordinates don’t satisfy the equation, then they are not the coordinates of that line. 

Slope Intercept Form Equation 

Now, we are confirmed that the slope-intercept form of a straight line is a neat and simplified way to find the equation of a line. In mathematics, the slope intercept formula is given as :

y = mx + k, or you can use any variable in place of these terms, but remember that:

  1. ‘y’ and ‘x’ always remain unchanged. They are the reason why this term is an equation.
  2. ‘m’ is defined as the slope of the line, and 
  3. ‘k’ is the ‘y’ intercept which has been talked about earlier. 

Some Examples of Slope Intercept Form

To ease all the theoretical knowledge mentioned above, let us look at some of the examples of slope intercept form and learn how to write an equation in slope intercept form.

Example 1: The slope of a line XY is (-1), and the y-intercept is (10). What is the equation of the line?

Answer: y = (-1) x + 10.

Example 2: The slope of a line XY is (7), and the line is passing from the origin. What is the equation of the line?

Answer: y = (7) x + 0 => y = 7x {Because when a line passes from the origin the x and y-intercept are (0,0)}

How to find the slope of a line?

You might find this one a tricky concept, but once you understand it, you will excel in finding the slopes of straight lines.

Method 1: If you know at what angle the line is inclined from the x-axis, you can find the slope by using simple trigonometry. Let us say that our line is inclined at an angle of ‘a’ from the x-axis then,

Slope ‘m’ = tan (a) 

Method 2: If coordinates of two points on the same line are given, we can easily find the slope by finding the ratio of the difference between the coordinates of the y-axis to the difference between the coordinates of the x-axis. For example: Let us say points (x, y) and (x1, y1) are in the same line, then 

Slope ‘m’ = (y – y1) / (x – x1)

For a deeper grasp of the notion, see the slope-intercept formula and its derivation below.

Derivation of Formula For Slope Intercept Form

Let us assume a random arbitrary point on the line: A (x, y). Also, let us consider that the slope of the line is ‘m’, and this line intersects the vertical axis (y-axis) at k such that the point C is (0, k). See the diagram for better clarification.

Utilizing the formula for finding slope when two points are given we have:

m = (y – y1) / (x – x1)

m = (y – k) / (x – 0)

m (x – 0) = y – k

mx = y – k

y = mx + k

This is a generic equation for a straight line that includes the slope and y-intercept. The slope-intercept form is the name given to this type of line equation. As a result, the slope intercept formula is created. Now you know how to write slope intercept form.

It is important to note that the slope-intercept formula cannot be used to get the equation of a vertical line. This is because a vertical line has no y-intercept.

Straight-Line Equation Using Slope Intercept Form

The two necessary parameters, that is, the slope ‘m’ of a line, and the y-intercept ‘k’, are utilized to establish the uniqueness of any line.

The procedures for determining a line’s equation using the slope-intercept form are outlined below.

Step 1: Write down the y-intercept, ‘k,’ and the line’s slope, ‘m.’ If the slope of a straight line is not supplied explicitly and other necessary data is available, we may use the slope formula to find it. (The slope formulas are mentioned above in the article) 

Step 2: Use the slope intercept formula to solve the problem: y = mx + k.

 Example: A line is inclined at an angle of 45° to the x-axis, and passes through the point (0, 10). Find the equation of the line.

Answer: We have, m = tan 45º = 1

Thus, the equation of this line is, y = mx + k

y = (1) x + (10)

y = x − 10

Isn’t the slope intercept form of a linear equation quite simple for you?

Now that we have covered all the theoretical aspects of this topic, let us look at some decent examples to ace the concepts of this article.

Examples on Slope Intercept Form

Example 1: Given the slope of a line is 1/2, and it crosses the y axis at (0, -3). Find the equation of the line.

Solution: We are given slope ‘m’ = 1/2,

Coordinates of point on y-axis where the line crosses = (0, -3) 

Therefore k = -3

Equation of the line => y = mx + k,

y = ½ x + (-3)

y = x/2 – 3

Answer: The equation of the line is y = x/2 – 3.

Example 2: Find the equation using the horizontal line slope intercept formula that intersects the y-axis at (0, 8). Solve it.

Solution: We are given that the line is horizontal, which means the angle of inclination ‘a’ is 0.

Thus tan (0) = 0

Coordinates of point on y-axis where the line crosses = (0, 8) 

Therefore k = 8

Equation of the line => y = mx + k,

y = 0 x + (8)

y = 8

Answer: The equation of the line is y = 8.That sums up the article about slope intercept form, how to find slope intercept form, how to write an equation in slope intercept form and slope intercept form of a linear equation. If you are still facing any doubts and think you have missed some concepts, then you can surf back to this article and find the answers to your queries in section-wise elaborated paragraphs. Moreover, do not forget to learn new concepts and practice them regularly.

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