How to plot a line parallel to a line with a distance of d between them ?

Question

Priya 2014-3-5

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评论： jaya prakash 2014-12-2

I have a line whose slope is m and y-intercept is c.

I wan to make a parallel line above and below to this line with at a distance of d between them.

Can anyone help ?

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Answer 1

Roger Stafford 2014-3-5

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My guess is that where Priya says "a parallel line above and below to this line with at a distance of d between them", the orthogonal distance between them is to be d, not the vertical distance. If so, the equations of the two lines would be:

Line above:

y = m*x + c + d*sqrt(1+m^2);

Line below:

y = m*x + c - d*sqrt(1+m^2);

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Priya 2014-3-5

Hi,

The solution was simple. Actually the slope of the line parallel to a given line, will be same as that of the given line and the intercept will actually be +/- distance d.

Thanks for efforts everyone

Roger Stafford 2014-3-6

Priya, I suggest you set m equal to a very large number such as m = 100, and make a plot of your three lines (using "axis equal") to see if a vertical displacement by d rather than an orthogonal one is what you are really after. The lines will look much closer together than your d value if a vertical displacement is used.

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