Daily Scribe

Today in class, we reviewed the concept of slope (rise over run). In addition to this, we learned a formula for finding the slope of a line when the coordinates of two points in the line are given. This is y2-y1/x2-x1.

Example: Find the slope of a line that passes through A(-2, 1) and B(5, 7). To solve this problem, you would call point A point 1, and point B point 2. Then you would substitute the variables for these numbers. We know x is the first number and y is the second number in each coordinate, so you know that x1 is -2 and x2 is 5. We also know that y1 is 1 and y2 is 7. Substitute these numbers for the variables in the formula, and you get 7 -1/5 -(-2) = 6/7. This is the slope. This formula would also work if you assigned the A-coordinates to 2 and the B-coordinates to 1. This way, the formula would be 1-7/-2-5=-6/-7, which is equal to 6/7.

Be cautious that you do not accidentally change the formula to y2-y1/x1-x2. This would mess up the whole thing. Also, be sure not to do x/y instead of y/x. If you have to find the slope of a line that passes through (2, 1) and (2, -4), the answer to this is undefined, because you will get the answer of -3/0. If you ever get an answer divided by 0, the answer is undefined, because you cannot divide anything by 0. A vertical line is undefined.