Sal is right but I understand the critique... which I might clarify as the importance of understanding the larger concept that slope is a comparison of the rate of change of one variable to another in specific order.
To take the example of price of an iPod vs. more memory. The slope is inverse depending on which variable you choose to plot on which axis. If you just watched Sal's one video, you would not understand why that is... your only context is 'rise over run'. If given sample data points and asked for a slope, you might not be able to figure out which way to plot it based on the question.
To be fair to Sal though, this was just a single video subtitled "Figuring out the slope of a line" and so Sal may have covered the larger concept and its importance in a different video.
To take the example of price of an iPod vs. more memory. The slope is inverse depending on which variable you choose to plot on which axis. If you just watched Sal's one video, you would not understand why that is... your only context is 'rise over run'. If given sample data points and asked for a slope, you might not be able to figure out which way to plot it based on the question.
To be fair to Sal though, this was just a single video subtitled "Figuring out the slope of a line" and so Sal may have covered the larger concept and its importance in a different video.