Wacko qusetion

[Mr Jody]

Originally Posted by mikiec

Point A to Point B = 26 inches. Point C is a fixed point in the distance.
If I move point A 1/8" to the left. How much do I have to move point B to maintain a straight line to point C?

The answer is 0".
It’s a trick question….sort of. The trick is in how you look at it.
You have to look at it as if line ABC goes from left to right. Originally, it’s 26” from A to B, and we’ll say X” from B to C, with point C being “in the distance” to the right. Something like this:
A_________________B_________________________C

After moving point A 1/8” to the left, they are all still in that same straight line ABC going from left to right. It's just that now it is 26 1/8” between A and B, and still X" between B and C. No point ever moved out of this line. Now it looks something like this (not to scale...and my attempt at a depiction just shifted B and C to the right, but you get the picture):
A_______________________B_________________________ C

[twobjshelbys]

Originally Posted by Mr Jody

The answer is 0".
It’s a trick question….sort of. The trick is in how you look at it.
You have to look at it as if line ABC goes from left to right. Originally, it’s 26” from A to B, and we’ll say X” from B to C, with point C being “in the distance” to the right. Something like this:
A_________________B_________________________C

After moving point A 1/8” to the left, they are all still in that same straight line ABC going from left to right. It's just that now it is 26 1/8” between A and B, and still X" between B and C. No point ever moved out of this line. Now it looks something like this (not to scale...and my attempt at a depiction just shifted B and C to the right, but you get the picture):
A_______________________B_________________________ C

That was the question I asked. If "to the left" is taken from the perspective that you are looking at the line ABC from perpendicular to the line then the answer is that B doesn't move because A' is along the original line and only the distance from AB to A'B changes. If you are looking straight into the line ABC the A' does move and I A' is a right angle to the line the new line of A'B and A'C need to be solved for the new triangle that is formed. You will first have to solve the A'AC triangle to get the new length of A'C. Then you will have to solve the A'AB to get the length of the new triangle A'BC Then you can solve the right angle of A'B to the A'C.

Again I assert that there are at least two possible answers (a different answer is to be had if the angle of A'A is not 180* or 90*) so there is insufficient information to answer it properly. Take the spec back to design engineering and ask them for clarification and engineered stamped drawings. Or overdrill B and let the drywallers patch over it.


I have a math degree... Physics too. I used to understand quantum mechanics but forgot.

[Car Nut]

Originally Posted by twobjshelbys

I have a math degree... Physics too. I used to understand quantum mechanics but forgot.

Perhaps your trying too hard. When solving triangles you need to know 3 things, I don't think 3 things are given.

[twobjshelbys]

Originally Posted by Car Nut

Perhaps your trying too hard. When solving triangles you need to know 3 things, I don't think 3 things are given.

Another hitch in the saddle. It wasn't stated whether it was "up". I'm thinking 10th grade planar geometry. So the answer could be that A'' is "higher". That wouldn't change the solution I described except the answer for B' could be "higher" rather than to the East. (or west, or south or north, depending on where you're standing when you determine which angle to the line A' is...)

Again, cry foul and say need more info

[Danr55]

it could be interpreted that way but the implication is that A moved off the line A B C to the left and created lines A C and B C. The question is asked about the length of the intercept. If there is no intercept, it becomes an invalid question and I've known Mikie long enough to realize he would not ask invalid questions.

Please Mikie, say it isn't so!

[Car Nut]

Originally Posted by Danr55

it could be interpreted that way but the implication is that A moved off the line A B C to the left and created lines A C and B C. The question is asked about the length of the intercept. If there is no intercept, it becomes an invalid question and I've known Mikie long enough to realize he would not ask invalid questions.

Please Mikie, say it isn't so!

At what angle from the straight line did A move away from its original point? You appear to have made an assumption that it is 90 degrees, where the "question" does not specify.

[mikiec]

It ain't so.

When A is moved, How far should B move, in the same direction as A, to maintain a straight line to C which does not move.

[Mike Brasfield]

If I were a moderator I would take this post off line.

[Danr55]

The question indicates that the point A moved 1/8" from line A B C. In order to be 1/8" from the line, it must be in a perpendicular direction. If you move 1/8" in anything other than 90 degrees direction , the resultant distance from line A B C to the relocated point A will be less than 1/8".

[Car Nut]

Originally Posted by Danr55

The question indicates that the point A moved 1/8" from line A B C. In order to be 1/8" from the line, it must be in a perpendicular direction. If you move 1/8" in anything other than 90 degrees direction , the resultant distance from line A B C to the relocated point A will be less than 1/8".

I think more correctly the vector length of 1/8 inch moved, it does not say which direction and there are 360 degrees of movement that can be considered. The question indicates point A is moved 1/8 inch, (from its original point, not line ABC) as quoted "If I move point A 1/8" to the left. How much do I have to move point B to maintain a straight line to point C?"

There is not enough information to satisfy the question. That is why it is (as in the thread title) a wacko question. You cannot solve it with exactitude.

[Danr55]

What determines how far you have to move point A to achieve "1/8" to the left"?

[Car Nut]

Originally Posted by Danr55

What determines how far you have to move point A to achieve "1/8" to the left"?

Move it 1/8 inch in any direction left of point A's original position intersected by it's vertical axis (between 6 o'clock to 12 o'clock). That doesn't imply perpendicular to the axis, merely a left heading. I may have taken too much license by assuming I am not standing on my head but we will go with it.

[Bernica]

You can't move Patrick (C)

[AL427SBF]

Originally Posted by Bernica

You can't move Patrick (C)

Nor would I want to, not even with a 10' pole.

[Ralphy]

So am I guessing right, your not looking for a number? Your wanting the equation/formula no matter where/distance C is? Damn so rusty in this ****! Hell I couldn't answer even I weren't! Does this have anything to do with where you put your beer?

Ralphy

[mikiec]

OK, it's time to stop the misery.

You have a straight line with points A B C along this line. Point A is at one end point C is at the other end. Point B is 26 inches from point A. Point B to point C is 10'(I think I used 10') Point A is moved to the left 1/8"

To maintain a straight line from ABC point B must move to the left. How far does point B move?

[AL427SBF]

A'
.......................................B'

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


Tangent (theta) = (opposite/adjacent) = (1/8")/146" = .000856
Arctan .000856 = 0.000855999791 rad

Tan (0.000855999791 rad) = Z/120"
Z = Tan (0.000855999791 rad) x 120"
Z = 0.000856 x 120"
Z = .103" (rounded)

[Car Nut]

Originally Posted by AL427SBF

A'
.......................................B'

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


Tangent (theta) = (opposite/adjacent) = (1/8")/146" = .000856
Arctan .000856 = 0.000855999791 rad

Tan (0.000855999791 rad) = Z/120"
Z = Tan (0.000855999791 rad) x 120"
Z = 0.000856 x 120"
Z = .103" (rounded)

So I guess you're assuming that the line ABC runs vertically, not horizontally as your diagram shows changing the movement of B to up not left. Right?

[AL427SBF]

BTW, Three Peeks had it right from the git-go ...

(120/146) x 1/8 = .103"

[mikiec]

You guys are amazing.

Thanks.