
19th March 2012, 10:24 PM

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Some maths qn
stuck at bi)
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19th March 2012, 10:32 PM

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Re: Some maths qn

 
19th March 2012, 10:44 PM

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Re: Some maths qn
Originally Posted by aj5122003 wow uni maths sio. It's just A level stuffs. lol.
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19th March 2012, 11:20 PM

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Re: Some maths qn
Which part of the question do you require assistance?

 
19th March 2012, 11:21 PM

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Re: Some maths qn
Originally Posted by whitecorp Which part of the question do you require assistance? part bi)
[10characters...]
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19th March 2012, 11:28 PM

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Re: Some maths qn
There you go:
Hope this helps. Peace.

 
20th March 2012, 12:34 AM

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Re: Some maths qn
Opps... i misinterpreted the question. i joined positional vector 3/2/7 to plane and says that it's parallel to line 1.
Oh yeah.. here's a DE question, can't show first part. o.o
=====================
another question. Can't do the one in red rectangle.
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Last edited by .Memo; 20th March 2012 at 03:35 AM.

 
20th March 2012, 09:38 AM

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Re: Some maths qn

 
20th March 2012, 07:29 PM

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Re: Some maths qn
Oh lololol! i got these from some maths site.
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20th March 2012, 10:15 PM

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Re: Some maths qn
I have a vectors question too!
How do I find the shortest distance between two planes? I've seen many formulas but I don't really understand how they work. Whitecorp, your vector's summary said something about putting a minus sign between the two modulus' if k1 and k2 have different signs. And about putting a plus sign if k1 and k2 have the same signs. I'm not sure how that works. o.O

 
20th March 2012, 10:36 PM

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Re: Some maths qn
When k1 and k2 are of the same sign ( either both positive or negative), then it means that both planes are on the same side of the origin.Hence, to find the distance between the two planes, it is a subtraction of the separate distances of the two planes to the origin. If one is positive while the other is negative, then the two planes are each on the opposite side of the origin; hence the distance between them is achieved by adding them.
Perhaps this in depth explanation on my site would help: http://www.whitegroupmaths.com/2010/...matters4.html
Hope this helps. Peace.
Last edited by whitecorp; 20th March 2012 at 10:36 PM.

 
20th March 2012, 10:41 PM

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Re: Some maths qn
Ah thanks! Is it possible to change the sign of k to make things simpler? Like, x  3y  2z = 4 change to x +3y + 2z = 4. I think that'll give a different answer though.

 
20th March 2012, 10:57 PM

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Re: Some maths qn
It won't make any difference even if you change signs. An example would make things clearer:
Eg. Find the distance between the planes x  3y  2z = 4 and x +3y + 2z = 3
So x  3y  2z = 4 (1) and x +3y + 2z = 3(2)
Notice that the normals to both planes (while parallel) are running in opposite directions. So
you either modify (1) to give x+3y+2z= 4 or modify (2) to give x3y2z= 3. This creates the realization that both planes are actually on the same side of the origin (and not on the opposite side as misleadingly given by the values 4 and 3 on the RHS of (1) and (2) ), and the distance between them is (43)/sqrt(14) =1/sqrt(14) units.
Bear in mind when we find distances between planes, we are finding distances between parallel planes, because the distance between two non parallel planes is simply zero. ( ie they will definitely intersect)
Hope this helps. Peace.
Last edited by whitecorp; 20th March 2012 at 11:01 PM.

 
20th March 2012, 11:03 PM

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Re: Some maths qn
Oh! I just realized n has to be in the same direction for both planes! Thanks for clarifying. :)

 
20th March 2012, 11:05 PM

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Re: Some maths qn

 
24th March 2012, 11:20 PM

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Re: Some maths qn
Originally Posted by whitecorp When k1 and k2 are of the same sign ( either both positive or negative), then it means that both planes are on the same side of the origin.Hence, to find the distance between the two planes, it is a subtraction of the separate distances of the two planes to the origin. If one is positive while the other is negative, then the two planes are each on the opposite side of the origin; hence the distance between them is achieved by adding them.
Perhaps this in depth explanation on my site would help: http://www.whitegroupmaths.com/2010/...matters4.html
Hope this helps. Peace. What happens if the point A lies directly above the origin?
Can we use the same concept? (Length of projection)
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26th March 2012, 02:25 PM

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Re: Some maths qn
Originally Posted by .Memo What happens if the point A lies directly above the origin?
Can we use the same concept? (Length of projection) If A lies directly above O, then the vector OA will be parallel to the normal vector of the plane (which can be seen very easily from the plane equation in either scalar product or cartesian form), in which case the magnitude of the vector OA will be the shortest distance from O to the plane. There is no need to use the concept of projection vectors. Hope this helps. Peace.

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