# Homework Help: Simpifying Help

1. Aug 28, 2009

### J-NCF

1. The problem statement, all variables and given/known data
Okay so here's the background.

g=(4pi^2/T^2)l

The instructions are:
Estimate the uncertainty in g using the uncertainty propagation for a general function. The specific formula you should obtain for delta g is:

#1 Δg= g (sqrt(Δl/l)^2 + (2 ΔT/T)^2)

The uncertainty equation is :

#2 ΔF=(sqrt (partial derivative of x)^2( Δx)^2 + (partial derivative of y)^2( Δy)^2)

So basically, make equation #2 look like #1, and solve for delta g.

So the question is, how do I simplify equation #2 to look like equation #1.

F=g , x=l, and y=T is those equations.

2. Relevant equations
g=(4pi^2/T^2)l

#1 Δg= g (sqrt(Δl/l)^2 + (2 ΔT/T)^2)

#2 ΔF=(sqrt (partial derivative of x)^2( Δx)^2 + (partial derivative of y)^2( Δy)^2)

3. The attempt at a solution

I know the derivatives of g in relation to l and T. The professor said something about using the derivatives and replacing g into the second equation, then factoring that g out, which is how equation #1 has a g in front of the square root. I can do that with the derivative of T, however Im left with a -2 instead of a positive 2. Im missing a l for the deriative of l (obviously), so I don't really know where to go from there.

Last edited: Aug 28, 2009
2. Aug 28, 2009

### tms

Show what you have done. It may be that you have made a simple algebra mistake, but no one can tell for sure without seeing what you have done. It may also be that by writing out everything explicitly you will see your error.