For an online calculator of Straight Line equations, go to: http://matrixlab-examples.com/equation-of-a-straight-line.html 1- Equation of a Straight Line 2a- A line AB is parallel to the X-axis when all of its points are at a constant distance from it. 2b- That equation would be y = k since all points whose ordinate is k would lie on that line. 3a- A line AB is parallel to the Y-axis when all of its points are at a constant distance from it. 3b- That equation would be x = k since all points whose abscissa is k would lie on that line. 4a- The slope is the vertical difference of two points divided by their horizontal difference. 4b- For horizontal lines y2 = y1, numerator = 0, and the slope is 0. 4c- For vertical lines: x2 = x1, denominator = 0, and the slope is undefined. 5a- This is the expression of the point-slope equation of a straight line. You need any point of the line and its slope. 5b- You can have more than one expression or equation, because you can always consider more than one point. 6a- In this example, point 1 is (-2, 1) and point 2 is (3, 5). 6b- The slope of this line is always 4/5, no matter which points or order we take. 6c- These two expressions represent the same line and just show different points. 7- The slope-intercept form takes into account the slope of a line and the y-intercept. 8- In this example, our y-intercept is 5, and our slope is 2. 9- In the general form we have a different approach. We can express the same line in many ways. We have coefficients A, B and C. 9a- The slope is the negative coefficient of x divided by the coefficient of y, that is --A/B. 9b- The y-intercept is the negative constant divided by the coefficient of y, that is --C/B. 9c- With the general form we can easily find the slope of a line and its y-intercept. 10- In this example the coefficient of x is 3, the coefficient of y is 7 and the constant is 5. Thus, the slope is -3/7 and the y-intercept is -5/7. Thank you for watching!