# Need help with vectos

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• Feb 1st 2013, 09:41 PM
Tutu
Need help with vectos

I thought to find the midpoint of B and the negative y-axis, and then equate the y-coordinate to sqrt(14) but that did not seem to be the way..
• Feb 1st 2013, 10:05 PM
chiro
Re: Need help with vectos
Hey Tutu.

(Hint: Try using Pythagoras' Theorem).
• Feb 1st 2013, 10:21 PM
Tutu
Re: Need help with vectos
But how, I do not know the coordinates of the other end of B?
• Feb 1st 2013, 10:27 PM
chiro
Re: Need help with vectos
You know the height of B and you know the hypotenuse.

Use the fact that a^2 + b^2 + c^2 = d^2 where you know d = SQRT(14) and a = -1, b = 2. (I'm using a 3D version of the Pythagoras' Theorem).
• Feb 1st 2013, 11:17 PM
Tutu
Re: Need help with vectos
Sorry, how did you get a^2 + b^2 + c^2 = d^2 ? And how did you get those values..?
Sorry
• Feb 1st 2013, 11:21 PM
chiro
Re: Need help with vectos
This is the form of the distance formula in three dimensions (as opposed to the one in two).

The hypotenuse is given in the question and the rest is found from the values in your diagram.
• Feb 1st 2013, 11:27 PM
Tutu
Re: Need help with vectos
I just went to search online,

they said a is the left right distance, b is the front back distance and c is the up down distance.
I understand why a^2 + b^2 + c^2 = d^2 but then shouldn't a be -1, b be -1, and c be 2?
How did you know sqrt 14 is the distance? The more I look at the diagram, it looks like the midpoint!
• Feb 1st 2013, 11:33 PM
chiro
Re: Need help with vectos
You are right in that a = -1 and b = -1 and you need to find a value of c where d = SQRT(14).
• Feb 1st 2013, 11:41 PM
Tutu
Re: Need help with vectos
I got c to be sqrt(12)?
• Feb 1st 2013, 11:43 PM
chiro
Re: Need help with vectos
That looks right.
• Feb 1st 2013, 11:48 PM
Tutu
Re: Need help with vectos
But from there, how do I find the two coordinates on the y-axis?
Sorry that I still cannot get this!
• Feb 1st 2013, 11:50 PM
chiro
Re: Need help with vectos
Find the y-point +- SQRT(12) of the B's y-point (which is -1 according to the diagram).
• Feb 2nd 2013, 12:17 AM
Tutu
Re: Need help with vectos
So it's -1+sqrt(12) and -1-sqrt(12)?
• Feb 2nd 2013, 12:20 AM
chiro
Re: Need help with vectos
Yes, that is the idea.
• Feb 2nd 2013, 12:27 AM
Tutu
Re: Need help with vectos
I found the answer sheet, it says the answer is (0,2,0) and (0.-4,0)!
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