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If the graph of the line y = ax + b passes through the points (4,5) and (8,17), what is a - b?

 Nov 22, 2018
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First, find the slope    = rise/run = (y1-y2)/(x1-x2) = (5-17)/ (4-8) = (-12)/-4 = 3    

   This is 'a'

  So the line , so far looks like

      y = 3 x + b      Now, let's put one of those x, y points in there to find 'b'

      5 = 3(4) + b

       5-12 = b    b = -7

 

So the equation for this line is   y = 3x -7      and    a-b = 3-(-7) = 3 + 7 = 10

 Nov 22, 2018

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