Why Does the Slope Formula Work?
Date: 10/29/2008 at 23:43:18 From: Paul =D Subject: Why does slope work To find the slope of a line, you do the formula y2-y1/x2-x1, when x1 is not equal to x2. But why does this formula work? I don't understand the relationship of the subtraction and division with slope. Is it simply an equation that creates different numbers which signify different angles?
Date: 10/30/2008 at 10:37:32 From: Doctor Ian Subject: Re: Why does slope work Hi Paul, In many cases, the best way to understand something is to re-invent it for yourself. Suppose I have two lines, like B C . . . . . . . . A We would say that AB is "steeper" than AC, right? But how could you QUANTIFY that? What kind of calculation could you do to attach a number to the idea of "steepness"? That's what we're doing with slope. We're trying to capture that concept in a calculation. Now, in the case of AB and AC, they both have the same amount of vertical travel ("rise"). But AB has less horizontal travel ("run"). If we divide rise by run, we get a larger number for AB, which is nice, because it makes sense that a larger value should correspond to a steeper line. Now, where does subtraction come in? Well, suppose we think of each line segment as the hypotenuse of a right triangle: B C . | . | . | . | . | . | . . | | A______________|_______________________| If we know the coordinates of A, B, and C, can you see how we can use subtraction to find the rise and run for each segment? - Doctor Ian, The Math Forum http://mathforum.org/dr.math/
Date: 10/30/2008 at 20:19:23 From: Paul =D Subject: Thank you (Why does slope work) Yay! I get it now. Rise and Run. Thank you!
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.