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external section formula

Posted: Fri Oct 07, 2016 2:37 am
by kh ibrahim
I'm facing trouble in the external section formula in vectors.here it is

Re: external section formula

Posted: Fri Oct 07, 2016 2:40 am
by kh ibrahim
the second part of that external section formula.

Re: external section formula

Posted: Fri Oct 07, 2016 2:41 am
by kh ibrahim
I don't know which is correct or why that would be correct.

Re: external section formula

Posted: Fri Oct 07, 2016 8:51 am
by Phlembac Adib Hasan
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.

Re: external section formula

Posted: Fri Oct 07, 2016 1:12 pm
by kh ibrahim
How can a ratio be negative?Is it because of different direction?

Re: external section formula

Posted: Sun Oct 09, 2016 10:02 am
by Phlembac Adib Hasan
Yeah. Vector lengths are direction sensitive.

Re: external section formula

Posted: Sun Oct 09, 2016 2:17 pm
by kh ibrahim
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?