Lines in the Plane
Read this section and work through practice problems 1-9.
Lines in the Plane
The first graphs and functions you encountered in algebra were straight lines and their equations. These lines were easy to graph, and the equations were easy to evaluate and to solve. They described a variety of physical, biological
and business phenomena such as 
relating the distance d traveled to the rate r and time t of travel, and 
for converting the temperature in Fahrenheit degrees (F) to Celsius (C).
The
first part of calculus, differential calculus, will deal with the ideas and techniques and applications of tangent lines to the graphs of functions, so it is important that you understand the graphs and properties and
equations of straight
lines.
Source: Dale Hoffman, https://s3.amazonaws.com/saylordotorg-resources/wwwresources/site/wp-content/uploads/2012/12/MA005-1.2-Lines-in-the-Plane.pdf
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