Riley, do you remember ``slope?' {{CMD_7}} Most definitely. ``Rise over run.'' {{CMD_8}} You know it. {{CMD_9}} ``Change in {{MATH_10}} over change in {{MATH_11}}.'' {{CMD_12}} That's right. {{CMD_13}} Brought to you by the letter ``{{MATH_14}}.'' {{CMD_15}} Enough! My important question is: could we define ``slope'' for a curve that's not a straight line? {{CMD_16}} Well, maybe if we ``zoom in'' on a curve, it would look like a line, and then we could call it ``the slope at that point.'' {{CMD_17}} Ah! And this ``zoom in'' idea sounds like a limit! {{CMD_18}} This is so awesome. We just made math! {{CMD_19}}