Equation for dividing a point AB internally/externaly (1 Viewer)

smallcattle

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(px2 + qx1) /(p+q) , (py2 + qy1) / (p+q)

just change to -p:q when dividing externally
 

tempco

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[px<sub>2</sub> + qx<sub>1</sub>]/[p + q]

Same as y.

If it's internally, keep p and q the same.

If it's externally, negative the smaller value... eg. 3:2 externally, make it 3:-2.

EDIT: Bah.
 

smallcattle

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nekkid said:
[px<sub>2</sub> + qx<sub>1</sub>]/[p + q]

Same as y.

If it's internally, keep p and q the same.

If it's externally, negative the smaller value... eg. 3:2 externally, make it 3:-2.

EDIT: Bah.

not necessarily
 

tempco

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Um, that's how I've learnt it... care to give an example where it's not true?
 

Managore

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wait - as a hypethetical, say if you had the following:

a point C that divides externally a and b in the ratio 1:2

What would, graphically, be correct:

C- - - - - - -A- - - - - - - - - - - - - - -B

C- - - - - - - - - - - - - - -A- - - - - - -B

A- - - - - - -B- - - - - - - - - - - - - - -C

A- - - - - - - - -- - -- - - B- - - - - -- C

A- - - - - - - - - - -B- - - - - - - - - - -C

C- - - - - - - - - - -A- - - - - - - - - - -B
 

tempco

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C - - - A - - - B
'_____'
'__________'


ACs 1 unit, and BCs 2 units.

I think.
 

Managore

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so if the ratio is 1:2 external its always on the A side? This has always confused me.. and now at nearly 11pm the night before I'm about to find out :)
 

mojako

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nekkid said:
Um, that's how I've learnt it... care to give an example where it's not true?
try with any values / questions.

it doesn't matter which one you make negative.
 

mojako

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Managore said:
so if the ratio is 1:2 external its always on the A side? This has always confused me.. and now at nearly 11pm the night before I'm about to find out :)
P divides AB in 3:2 externally means:
AP is the 3, PB is the 2 (the shorter one)
(also this means B is between A and P)

P divides BA in 3:2 means:
BP is the 3.
 

tempco

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Yer I think so... and if the ratio was 2:1, it would be:

A - - - B - - - C

and having the lesser ratio being negative makes sense... AC in the + direction ( --> ) and CB in the - direction ( <-- ). So in the equation it'd be 2:-1.

As for 1:2, AC is in the - direction ( <-- ) and CB is in the + direction ( --> ), so it would be -1:2.

*shrugs* I have no idea what I'm talking about.

EDIT: Hrm... it doesn't make a difference. o____O
 
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mojako

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it doesnt matter which +ve direction you choose

btw to those who are not desperately needing to study, I suggest you go to sleep soon.
maths needs concentration.
also dont wake up early tomorrow.
 

CrashOveride

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dont listen to mojo guys
ill be on here 5am, if u need help just post ill help :)
 

Rorix

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doing ratio questions by inspection is cooooool


but ill have to resort to algebra to get both marks, probably:(
 

Managore

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Ah I finally get it.. I like doing it by inspection, makes more sense to me than a formula, but I'll state the formula as well, in case I get inspection wrong. Thanks everyone
 

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