- #1

- 20

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I have some simple 3d data like,

Code:

```
point 1: x1 = 5.8573375, y1 = -4.17885, z1 = 2.338175
point 2: x2 = -3.26132, y2 = 1.28276, z2 = 0.931583
```

I need to be able to extend the line from point 1 through point 2 to some additional distance.

There are a few posts on stackexchange, but they are all in c++ code and I couldn't get results in excel that look correct. Maybe it's just too late in the day. What I found was more or less,

Code:

`x3 = x2 * M - x1, y3 = y2 * M - y1, z3 = z2 * M - z1 where M is a multiplier`

For the example I gave above, this gives me a point that is no where near anything that resembles an extension of the line from point 1 to point 2.

Code:

`x3 = 2.92866875, y3 = 4.82023, z3 = -1.8723835`

Maybe I just got the parenthesis wrong or something lame like that. This seems like it should be very simple but I'm not sure if I need to find the slope first or if something like the above will work.

Can someone point me to the correct formula?

Thanks,

**LMHmedchem**