To find the slope of a non-vertical line you need two points on the line. Subtract the second y-value from the first y-value, and subtract the second x-value from the first x-value, then divide the first number calculated by the second number calculated. As a formula, it looks like this: slope = (first yvalue - second yvalue) / (first xvalue - second xvalue) Alternatively, if you know calculus, the slope at some x-coordinate a of the function f(x) = d/dx[f(x)] evaluated at a = f'(a).
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