
Michael R. answered 01/06/23
Teacher of Mathematics with 18 years of Experience
Hi Jessica,
The slope (typically labeled "m".) of a line is a measure of its "steepness" and is defined as the ratio of rise to run. In other words, (how far up or down)/(how far over).
If we know two points on a line, the rise between them is calculated by subtracting the y-coordinates, while the run is calculated by subtracting the x-coordinates.
Therefore, the slope formula is written as, m = (y2 - y1)/(x2 - x1).
Where (x1, y1) and (x2, y2) are two points known to be one the line.
Notice that subscripts (the little "dropped" numbers) don't represent any arithmetic operation, their only purpose is merely to distinguish the coordinates of one point from the other.
Students often ask which is point 1 and which is point 2 or does it even matter.
The answer is it doesn't matter which is which AS LONG AS YOU'RE CONSISTANT!
Personally, I recommend reading the graph from left to right.
That is, I use the left-most point 1 and the point to the right as point 2.
This trick of mine guarantees that my run (the denominator) is always positive.
In this problem the points are (1, 8) and (6, 5)
The left-most point is the one with the smaller x, so point 1 is (1, 8) and point 2 is (6, 5)
This means that x2 = 6, y2 = 5, x1 = 1 and y1 = 8.
If we plug these numbers into the formula, we get m = (5 - 8)/(6 - 1) = -3/5.
I hope this helps.