Error Propagation: x/(y-z) Uncertainty

[newbe318]

Homework Statement

Suppose you measure three numbers as follows:

Homework Equations

x= 200. +-2.
y= 50. +-2.
z= 40. +-2.

where the three uncertainties are independent and random. Use step-by-step propagation to find the quantity
q= x/(y-z) with its uncertainty.

The Attempt at a Solution

I do not know what to do. The only thing I am thinking of doing is taking the derivatives of the func., q= x/(y-z), with respect to x, y, and z, ... and ... that's it. I'm stuck. Help, please?

 

[Student100]

Homework Statement

Suppose you measure three numbers as follows:

Homework Equations

x= 200. +-2.
y= 50. +-2.
z= 40. +-2.

where the three uncertainties are independent and random. Use step-by-step propagation to find the quantity
q= x/(y-z) with its uncertainty.

The Attempt at a Solution

I do not know what to do. The only thing I am thinking of doing is taking the derivatives of the func., q= x/(y-z), with respect to x, y, and z, ... and ... that's it. I'm stuck. Help, please?

How is error propagated in the (y-z) part? That will produce some new uncertainty a, which you then propagate for x/a. How far have you actually gotten?

 

[newbe318]

I didn't get very far.
I skipped that problem and continued with my other homework problems.

 

[Student100]

I didn't get very far.
I skipped that problem and continued with my other homework problems.

Do you know how error is propagated in subtraction?

 

[newbe318]

You add them?

 

[Student100]

You add them?

You add the sum of the uncertainties squared, then take the square root. Is it apparent why?

So what's the uncertainty of a?