Question 285651
Given two points (x1, y1) and (x2, y2), derive the equation of the line that passes through those two points and write
it in the form y = mx + b. This is called the slope-intercept form of the equation of the line because the two parameters m and b
represent the slope and y-intercept of the line. 
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slope = m = (y2-y1)/(x2-x1)
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The line passes thru (x1,y1) so substitute the point
values and the slope values into y = mx+b to get:
y1 = {{y1-y2]/[x2-x1]}[x1] + b
b = y1 - {{y2-y1]/[x2-x1]}[x1]
b = y1 - {x1y2-x1y1}/{x2-x1}
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b = [y1(x2-x1) - (x1y2-x1y1]/[x2-x1]
b = [x2y1-x1y1-x1y2+x1y1]/[x2-x1]
b = [x2y1-x1y2]/[x2-x1]
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Equation:
y = [(y2-y1)/(x2-x1)]x + [x2y1-x1y2]/[x2-x1]
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Cheers,
Stan H.