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Graphs of Linear Equations

# Determining the equation of a line from a graph

Many times, you'll have the graph of an equation shown to you and you'll need to find the equation.  This seems a very daunting task, but it's actually quite easy!

We can use the slope-intercept formula: y = mx + b

• To find b, remember is the point when the line crosses the y axis
• To find the value of the slope, you compute the rise over the run. Remember you can also determine the equation of a line from its graph if you get two points of the line.

Find the equation of the line: We can calculate m because the line goes through points (-2,0) and (0,3). That is .
We can calculate b because the y-intercept point is (0,3). That is b=3.
The equation of the line is: .

 The equation of the line graphed in the accompanying figure is: y= x+