- 1). Subtract the y-coordinate of the first point on a line from the y-coordinate of the second point. For example, if your line had the points (5,2) and (6,4), you would subtract 2 from 4 to get 2.
- 2). Subtract the x-coordinate of the first point on a line from the x-coordinate of the second point on the line. For example, if your line had the points (5,2) and (6,4), you would subtract 5 from 6 to get 1.
- 3). Divide the difference in y-coordinates by the difference in x-coordinates to calculate the slope of your line. This will also be the slope for any line parallel to the line in this example. Here you would divide 2 by 1 to find the slope of the line, and any line parallel to it, will be 2.
- 4). Find the opposite inverse of the slope to calculate the slope of a perpendicular line. To find the opposite of a number, change the sign (positive to negative or negative to positive). To find the inverse, flip the numerator and the denominator. Finishing the example, to take the opposite inverse of 2, you would change the number from a positive number to a negative number and then flip the numerator and denominator (a whole number is the same as that number over 1) to get -1/2. Therefore, the slope of any line perpendicular to a line with a slope of 2 would have a slope of -1/2.
previous post