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Asked by as hz on 27 Oct 2013

Hi,

I have a line between with starting point of [X1,Y1] and ending point [X2,Y2] and I would like to draw a parallel line with the same length and angle(to the x axis) that pass through 3rd point [X3,Y3]. How can I do it?

Thanks.

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Answer by Image Analyst on 27 Oct 2013

Sounds a lot like homework so I'll just get you started. It's really just 10th grade math. The slope of the first, reference line is

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

So the second line has the same slope but you just use the point-slope formula of a line:

y - y3 = slope * (x - x3)

or

y = slope * (x - x3) + y3

Now, there is an **infinite number of endpoints pairs** for that second line that will satisfy the requirement that it is parallel and has the same length. To go any further will require another constraint/requirement, such as the angle from the original endpoint to the new endpoint to the new line is 90 degrees, or something like that. Otherwise, like I said, it could be anywhere.

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