In short
The slope of a line is its steepness: the change in divided by the change in between any two points, .
A line that rises from left to right has a positive slope. A line that falls has a negative slope. A horizontal line has slope , and a vertical line has no slope defined. The equation gives the slope and the -intercept . Two lines are parallel if their slopes are equal and perpendicular if the product of the slopes is .
Through and the slope is , so the line is , which is .
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