# Problems with propagation of error

#### bobey

##### New member
I have problem regarding the propagation of error since the equations involving mixtures of multiplication, division, addition, subtraction, and powers. Please help me to clarify whether my attempts are right or wrong.

#### Sudharaka

##### Well-known member
MHB Math Helper
I have problem regarding the propagation of error since the equations involving mixtures of multiplication, division, addition, subtraction, and powers. Please help me to clarify whether my attempts are right or wrong.

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Hi bobey,

I think you should review how to calculate the propagation of errors. One of the basic things that you should remember is to neglect the constant values of the formulas when deriving the error propagation formula. For example take your Question 1.

$D=-\frac{L}{4m}$

Now, the error propagation formula would be,

$\frac{\Delta D}{D}=\sqrt{\left(\frac{\Delta L}{L}\right)^2+\left(\frac{\Delta m}{m}\right)^2}$

Even if you have the formula, $$\displaystyle D=\frac{L}{m}$$ you get the same error propagation formula above. The constant $$-\frac{1}{4}$$ have no significance.

Read this and this to find out how to derive the error propagation for any given formula.

Kind Regards,
Sudharaka.

Last edited:

#### CaptainBlack

##### Well-known member
Hi bobey,

I think you should review how to calculate the propagation of errors. One of the basic things that you should remember is to neglect the constant values of the formulas when deriving the error propagation formula. For example take your Question 1.

$D=-\frac{L}{4m}$

Now, the error propagation formula would be,

$\frac{\Delta D}{D}=\sqrt{\frac{\Delta L}{L}+\frac{\Delta m}{m}}$
I would check this if I were you.

CB

#### bobey

##### New member
Problems with propagation of error for multiple variables

please help by telling me whether my approach to solve the problems are right or wrong. please refer to the ATTACHMENT for the questions and my approaches...

question 1

question 2

#### CaptainBlack

##### Well-known member
Re: Problems with propagation of error for multiple variables

please help by telling me whether my approach to solve the problems are right or wrong. please refer to the ATTACHMENT for the questions and my approaches...

question 1
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For this one you should not need the square and square root, they cancel, and anyway you only use a root sum of squares composition of errors when there is more than one variable involved.

CB

#### CaptainBlack

##### Well-known member
Re: Problems with propagation of error for multiple variables

please help by telling me whether my approach to solve the problems are right or wrong. please refer to the ATTACHMENT for the questions and my approaches...