Linear Equations or Equations of Straight Lines can be written in different forms.
In this lesson, we will learn
y = mx + b, where m is the slope of the line and b is the y-intercept.
The y-intercept is the y-coordinate of the location where line crosses the y axis. This is the point when x = 0 and y = b.
Vertical lines, having undefined slope, cannot be represented by this form.
The slope-intercept form is useful when we are given the slope and y-intercept of a line and we need to write an equation for the line.
It is also useful because we can read the slope and y-intercept from the equation. Often, when we are given equations in other forms, we can rewrite it in slope-intercept form to get the slope and y-intercept.
The slope-intercept form is also useful when we need to draw the line on a graph.
More examples, videos and explainations about the slope-intercept form and how it can be used.
y − y1 = m(x − x1)
where m is the slope of the line and (x1, y1) is any point on the line.
The point-slope form shows that the difference in the y-coordinate between two points on a line is proportional to the difference in the x coordinate. The proportionality constant is the slope of the line, m.
The point-slope form is useful when we are given a point on a line and the slope and we need to get the equation of the line.This video shows an example of finding the equation of a line using point-slope form when given two points.
Ax + By + C = 0, where A or B can be zero, but not both at the same time.
The equation is usually written so that A ≥ 0. The graph of the equation is a straight line, and every straight line can be represented by an equation in the above form.
If B is not zero, then the slope of the line is −A/B and the y-intercept is −C/B.
If B is zero, then the line Ax + C = 0 is a vertical line with a x-intercept of −C/A.
If A is zero, then the line By + C = 0 is a horizontal line with a y-intercept of −C/B.
The General Form is useful when we want to write equations for vertical lines which is not possible in slope-intercept form or point-slope form. For example, 2x + 5 = 0.
Ax + By = C, where A or B can be zero, but not both at the same time. A, B and C are integers and A ≥ 0. A, B and C have no common factors other than 1.
When is Standard Form useful?
We will look at how to convert between the different forms of equation.This video shows how to convert from Standard Form to Slope Intercept Form
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