From algebra I:

Equation of a line:

y = mx + b

what you know:

x1,y1
x2,y2

Therefore:

y1 = mx1 + b

y2 = mx2 + b

Subtracting:

y1 - y2 = m(x1 - x2)

if x1 == x2 then it is a vertical line on y

therefore (assuming x1 != x2)

m = (y1 - y2)/(x1 - x2)

substituting in first equation:

y1 = (y1 - y2)/(x1 - x2)x1 + b

b = y1 - (y1 - y2)/(x1 - x2)x1

therefore the equation of a line (assuming x1 != x2) is:

y = (y1 - y2)/(x1 - x2)x + (y1 + y1 - y2)/(x1 - x2)x1

--

flounder

In reply to Re: Plotting A Line by flounder99
in thread Plotting A Line by mdog

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