Slope: Alternate Interpretation

Recall that the slope of a line is a number that simply tells us how STEEP that line actually is. You've already learned that slope is the RATIO of the RISE to the RUN between any two points that lie on the line. Here may be a more meaningful interpretation of the phrase "slope of a line" for some of you: The slope of a line is the amount by which the output (y-value) of the line changes when the input (x-value) increases by 1 unit. Interact with the applet below for a few minutes. Feel free to drag the WHITE POINT up and down and ZOOM IN or ZOOM OUT if you need to. Answer the questions that follow. (Note color changes that may occur!)

What causes the slope of the line to appear purple?

What causes the slope of the line to appear red?