Alrighty, graphs are my favorite! First of all, you only need two lines to find the slope without even graphing! Isn't that neat?
Let's see..the example you gave. Let's take two of those points (-1,-1) and (0,0).
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If you have used \(\displaystyle \L{}m=\frac{y_1-y_2}{x_1-x_2}\) yet, then you can just sub in the points like so:
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\(\displaystyle \L{}m=\frac{(-1-0)}{(-1-0)}\); \(\displaystyle \L{}m=\frac{-1}{-1}=1\)
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So, that means \(\displaystyle \L{}m=1\) and since m is your slope, 1 is the slope of your line.
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If you haven't heard of this formula before, then simply plot all of those points and connect them to make the line. Then, just see how far up (this is the top of the fraction or "the rise" and will be positive if you are going up and negative if you are going down.) you have to go from one point to the next and then how far left (which will be a negative number in the bottom half of your fraction or "the run") or right (which would be a positive number in the bottom).
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Did I answer anything for you? If I was too confusing or didn't answer your question, please just let me know and I will explain better.
