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Equation of a Line (Point-Slope)

This calculator helps you find the equation of a straight line when you know one point on the line and its slope. It will output the equation in the familiar slope-intercept form: y = mx + b.

Enter the x-value of the known point.

Enter the y-value of the known point.

Enter the slope of the line.

How it works

This calculator helps you find the equation of a straight line when you know one point on the line and its slope. It will output the equation in the familiar slope-intercept form: y = mx + b.


The Formula

The point-slope form of a linear equation is y - y₁ = m(x - x₁), where (x₁, y₁) is a known point and m is the slope. To convert this to slope-intercept form (y = mx + b), you rearrange the equation to solve for y.

Worked Example

  1. Example: Find the Equation

    Given a point (3, 5) and a slope of 2. We use y - y₁ = m(x - x₁). So, y - 5 = 2(x - 3). Distribute the slope: y - 5 = 2x - 6. Add 5 to both sides: y = 2x - 1. Here, m = 2 and b = -1.


Tips, Assumptions & Limitations

  • Ensure your point coordinates (x, y) and slope (m) are entered correctly.
  • Remember that 'b' is the y-intercept, where the line crosses the y-axis.
  • A positive slope means the line rises from left to right; a negative slope means it falls.
FAQ

The point-slope form is y - y₁ = m(x - x₁), where 'm' is the slope and (x₁, y₁) is a specific point on the line. It's a handy way to write a linear equation if you have these two pieces of information.

Once you have the point-slope form, simply distribute the slope 'm' on the right side, then isolate 'y' by moving the y₁ term to the right side of the equation. This will give you y = mx + b.

Yes, absolutely! This calculator is designed to work with both positive and negative values for the slope and the x and y coordinates of your point. Just enter them as usual.

Companion article

Equation of a Line from Point and Slope: Your Guide to y = mx + b

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How this calculator works

Understanding how to find the equation of a straight line is a core skill in algebra. Often, you're given a point that the line passes through and its slope. This guide will walk you through the process, from the point-slope form to the more familiar slope-intercept form (y = mx + b).

Explanation

A straight line can be uniquely defined by a single point it passes through and its slope. The point-slope form, y - y₁ = m(x - x₁), is a direct way to express this relationship. Here, 'm' is the slope, and (x₁, y₁) represents the coordinates of the known point. By rearranging this equation, you can easily get the line into the slope-intercept form, which clearly shows the slope and y-intercept.

Formula

The Point-Slope Form: y - y₁ = m(x - x₁) Where:
• (x₁, y₁) is a known point on the line
• m is the slope of the line To convert to Slope-Intercept Form (y = mx + b):
1. Distribute 'm' into (x - x₁). 2. Add y₁ to both sides of the equation.

Worked example

Let's say you have a line that passes through the point (2, 7) and has a slope of 3. Using the point-slope form: y - 7 = 3(x - 2). First, distribute the 3: y - 7 = 3x - 6. Then, add 7 to both sides to isolate y: y = 3x + 1. This is the equation in slope-intercept form.

How to use this tool

Our Equation of a Line (Point-Slope) Calculator makes this process simple. Just enter the x-coordinate of your known point into the 'Point X-coordinate (x₁)' field, the y-coordinate into 'Point Y-coordinate (y₁)', and the slope into the 'Slope (m)' field. The calculator will instantly display the equation of your line in the y = mx + b format, along with the calculated slope and y-intercept.

Frequently asked questions

Why is y = mx + b called slope-intercept form?
It's called slope-intercept form because 'm' directly represents the slope of the line, and 'b' directly represents the y-intercept (the point where the line crosses the y-axis). This form makes it easy to visualize and graph the line.
What if the slope is zero?
If the slope (m) is zero, the line is horizontal. The equation will simplify to y = b, where 'b' is the y-coordinate of every point on the line. Our calculator handles this case correctly.
Can I use this for parallel or perpendicular lines?
Yes! If you know a line is parallel to another, it shares the same slope. If it's perpendicular, its slope is the negative reciprocal of the other line's slope. You can calculate the new slope and then use this tool.

Read the full guide →

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