external section formula

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kh ibrahim
Posts: 17
Joined: Mon May 09, 2016 11:18 am

external section formula

I'm facing trouble in the external section formula in vectors.here it is
Attachments external section formula.I don't know which is correct.need the solution
rps20161007_023032.jpg (125.21 KiB) Viewed 1197 times

kh ibrahim
Posts: 17
Joined: Mon May 09, 2016 11:18 am

Re: external section formula

the second part of that external section formula.
Attachments external section formula.the second part is here.picture
rps20161007_022523.jpg (29.54 KiB) Viewed 1196 times

kh ibrahim
Posts: 17
Joined: Mon May 09, 2016 11:18 am

Re: external section formula

I don't know which is correct or why that would be correct.

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Re: external section formula

Both of the formulae are correct. $C$ is not on the same end of $\vec{AB}$ in both proofs. That's why the formula changes.

Actually, there is no special formula called external section formula. It's just the internal section formula with one of the ratios being negative.
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kh ibrahim
Posts: 17
Joined: Mon May 09, 2016 11:18 am

Re: external section formula

How can a ratio be negative?Is it because of different direction?

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Re: external section formula

Yeah. Vector lengths are direction sensitive.
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kh ibrahim
Posts: 17
Joined: Mon May 09, 2016 11:18 am

Re: external section formula

Lets talk out of vectors.Supposing if a point C divides a line segment AB externally what would it mean?Will it mean C is closer to A or B?Why would it mean so?