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... 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 =(x2 + y2 + z2)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(x2) = 2x3(E(x))2 which is the same for the error in y2, and the same for the error in z2. 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 = a2(E(x))2 + b2(E(y))2 + c2(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 = axb 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 = d1/2 Is this a correct way of going about it ? Thank you!