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Equations of Lines

Equations of Lines. Equations to Remember. Slope-Intercept Form. Useful for graphing since m is the slope and b is the y-intercept. Point-Slope Form. Use this form when you know a point on the line and the slope

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Equations of Lines

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  1. Equations of Lines

  2. Equations to Remember Slope-Intercept Form • Useful for graphing since m is the slope and b is the y-intercept Point-Slope Form • Use this form when you know a point on the line and the slope • Also can use this version if you have two points on the line because you can first find the slope using the slope formula and then use one of the points and the slope in this equation. General Form • Commonly used to write linear equation problems or express answers

  3. Parallel and Perpendicular Remember parallel lines have the same slopes so if you need the slope of a line parallel to a given line, simply find the slope of the given line and the slope you want for a parallel line will be the same. Perpendicular lines have negative reciprocal slopes so if you need the slope of a line perpendicular to a given line, simply find the slope of the given line, take its reciprocal (flip it over) and make it negative.

  4. Story Problems These will be linear models. When you read the problem look for two different variables that can be paired together in ordered pairs. Example: The total sales for a new sportswear store were $150,000 for the third year and $250,000 for the fifth year. Find a linear model to represent the data. Estimate the total sales for the sixth year. (5, 250,000) (3, 150,000) We now have two points and can determine a line that contains these the points (on the next screen) Total sales depend on which year so let’s make ordered pairs (x, y) with x being the year and y being the total sales for that year.

  5. (3, 150,000) (5, 250,000) We’ll want to use the point-slope equation First we need the slope Now we have all the pieces we need so we can plug them in We now have an equation to estimate sales in any given year. To estimate sales in the sixth year plug a 6 in for x.

  6. Acknowledgement I wish to thank Shawna Haider from Salt Lake Community College, Utah USA for her hard work in creating this PowerPoint. www.slcc.edu Shawna has kindly given permission for this resource to be downloaded from www.mathxtc.com and for it to be modified to suit the Western Australian Mathematics Curriculum. Stephen Corcoran Head of Mathematics St Stephen’s School – Carramar www.ststephens.wa.edu.au

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