I didn't really know on the forum to put this, it isn't really homework or coursework, but it is a very small part of a project im doing for uni, so essentially it could be worth marks so here it is, anyway...(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

Im rubbish at combining errors and was wondering if someone could just guide me on this sepcific issues... Im trying to get the error in a pythagorean distance, i.e the error in...

Distance =(x^{2}+ y^{2}+ z^{2})^{1/2}

Now I have all the errors of x, y and z respectively. My problem is that I dont think I am combining the error corrrectly, see section3...

3. The attempt at a solution

So what I am doing is to say...

1. x*x, y*y and z*z are all combinations of errors, for all of which I have been using...

z = axy

where a=1, x=x, y=x, such that...

E(x^{2}) = 2x^{3}(E(x))^{2}

which is the same for the error in y^{2}, and the same for the error in z^{2}.

2. next I say, find the error in x*x + y*y + z*z, for which I use...

z = ax + by + cz where a=b=c=1

where the error is...

(E(z))^{2}= a^{2}(E(x))^{2}+ b^{2}(E(y))^{2}+ c^{2}(E(z))^{2}

I work all this through and get a value for the error in x*x + y*y + z*z, then...

3. error in distance = (x*x + y*y + z*z)^{1/2}, for which I use...

z = ax^{b}where a=1, b=0.5

this uses the formula E(z)/z = bE(x)/x

So I rearrange all this, calculate the individual errors, but I get a number that is just plain wrong.

So, in summery of how I do it...

1 - Work out the error in

----a = x*x

----b = y*y

----c = z*z

2 - work out the error in...

----d = a + b + c

3 - work out the error in...

----e = d^{1/2}

Is this a correct way of going about it ?

Thank you!

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# Homework Help: Combining Errors

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