 ###### Alissa Fong

MA, Stanford University
Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

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# Point-Slope Form of a Line - Problem 3

Alissa Fong ###### Alissa Fong

MA, Stanford University
Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

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In order to write the equation of a line, you need to know the slope and a point that the line contains. Parallel lines have the same slope, perpendicular lines have opposite sign reciprocal slopes (like -2 and 1/2.) If you're only provided with two points, you'll need to use the slope formula (y2 - y1)/(x2 - x1) and then you can use either point to find the equation of your line. Start with the point slope form, y - y1 = m(x-x1) and then solve for y if you want slope-intercept form. Vertical lines always have equation x = constant, and horizontal lines have the equation y = constant.

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