Another point distance question.

Question

Please excuse my complete ignorance on what should really be something I can work out myself but hoping someone would be kind enough to help.

I am trying to solve the problem where I wish to calculate a point along a line n distance from point p1.

I have looked at the questions How do I find a point a given distance from another point along a line? and How to find a point between two points with given distance? and have tried to apply them to a trivial case for which I know the answer but seem to be stuck.

I have used a trivial example to test where I have point 1 which is 1,1 and point 2 which is 5,1 and I want to calculate 1 step from point 1 which I expect would give me the result 2,1.

When I attempted to calculate these values based on the above formulas I did the following:

y3 = 1 + 1/4 * (1-1)

x3 = 1 + 1/4 * (5-1)

Which gave me the result 2,1.25

Clearly I have messed up somewhere but I am not sure where, can anyone be kind enough to point me in the right direction?

you get $x_3=1+\frac14(5-1)=1+\frac44=2$ and $y_3=1+\frac14(1-1)=1+0=1$ — J. W. Tanner, Sep 30 '21 at 16:42
@JoséCarlosSantos I am not sure where this question is supposed to be and I am happy to change it. I apologise if I have put it in the wrong category — Maxim Gershkovich, Sep 30 '21 at 16:45
It seems to me that [tag:analytic-geometry] is a much better choice. — José Carlos Santos, Sep 30 '21 at 16:47
@J.W.Tanner Thank you for that and I really do appreciate everyones super quick response, just do try to keep in mind that things that seem trivial for you guys are far from for us mere mortals... — Maxim Gershkovich, Sep 30 '21 at 16:53

score 1 · Accepted Answer · answered Sep 30 '21 at 16:45

1

Clearly I have messed up somewhere but I am not sure where

It appears that you computed $1-1=1$ instead of $1-1=0$ when applying the formula for $y_3$,

so you got $1.25$ instead of $1$.

answered Sep 30 '21 at 16:45

J. W. Tanner

60,406

Of course. I am a complete idiot. I didnt compute 1-1 = 1. I Simply ignored BODMAS. So basically its 1 + (1/4 * 0) = 1? Instead I added 1 + 0.25 first.... Thank you!!!! – Maxim Gershkovich Sep 30 '21 at 16:50
1

Yes, it's $1+\frac14(0)=1$ – J. W. Tanner Sep 30 '21 at 16:52
Thank you again, much appreciated! and sorry for wasting your time – Maxim Gershkovich Sep 30 '21 at 16:58

Another point distance question.

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