# Homework Help: Tool or software able to find the length of the sides

1. Jul 14, 2012

### hgphtgi

Hello there!

I'm looking for such a tool or software able to find the length of the sides ( xa, xb, xc and xd ) each time i moved the point x, hint that a, b, c and d are fixed and known

please help me this is the last problem in my project

REGARDS

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2. Jul 14, 2012

### CWatters

Do I get a mark for working out that this is to do with suspending a TV camera over a football pitch? Well even if it isn't lets pretend it is..

Best approach I reckon is to assume that the plane abcd is the pitich or rather a plane the same size raised above it. Lets call that the xy plane. The camera is then at position x,y,z where z is the height above the pitch (or below the suspension points abcd depending on how you look at it)

Pick one of the points (eg "a" as the origin).

Then pythagorous says the length of the "a-camera" wire is given by

(a-camera)2 = x2 + y2 +z2

The rest I'll leave to you.

3. Jul 14, 2012

### hgphtgi

thanks a lot CWatters

sorry i am study diploma ( 1 sem ), i mean i am not an expert u know. please help me to get the solution.

regards

4. Jul 15, 2012

### haruspex

You haven't indicated how you control or know the position x. If you know its x, y, z coordinates relative to a, b, c and d then just apply Pythagoras' Theorem as already suggested. If not, what?
Btw, the four distances are related by xa2 + xd2 = xb2 + xc2.

5. Jul 15, 2012

### hgphtgi

tnx haruspex for ur reply

in fact i know the height of point x, however i am not expert in mathematics, can you please support your answer with an example.

sorry friend but i hv no choice to understand except this way

regards

6. Jul 15, 2012

### CWatters

If you can't understand pythagorous then this is going to be very difficult.

Start with a 2D problem..

Draw a rectangle on the ground with sides x and y. Then the length of a diagonal d is given by pythagorous as

d2=x2 + y2

or d= sqrt(x2 + y2)

Now imagine you have a pole with a point Z on it stuck in the ground at corner x,y. Draw the triangle from the origin 0,0,0 to x,y,0 to x,y,z and back to the origin. Note it has sides of length d and z

The length of the "3D diagonal" big D from the origin (0,0,0) to (x,y,z) is given by

D2= d2 + z2

but we know d2 = x2 + y2

so D2= x2 + y2 + z2

This gives you the length of one of the wires from the origin to point z.

eg

D = Sqrt(x2 + y2 + z2)

Working out the length of the other wires in terms of x,y,z is only slightly more complicated

Last edited: Jul 15, 2012
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