# How do you find the approximate uncertainty of a circle of radius 3.8x10^4?

1. Mar 7, 2010

### steve snash

how do you find the approximate uncertainty of a circle of radius 3.8x10^4????

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

how do you find the approx uncertainty for a circle with radius 3.8x10^4, i have no idea how to get the final uncertainty of the circle the radius uncertainty is 0.1x10^4

area of a circle is pie*r^2? so that means the area of the circle should be 4.5x10^9 isnt it???

3. The attempt at a solution i figured that because there is only one variable that the uncertainty would just be 0.1x10^4, how do you work out the final uncertainty properly?????

2. Mar 7, 2010

### steve snash

Re: how do you find the approximate uncertainty of a circle of radius 3.8x10^4????

3. Mar 8, 2010

### willem2

Re: how do you find the approximate uncertainty of a circle of radius 3.8x10^4????

One way to do this that always works is to calculate the area for the minimum and for the
maximum radius to find out what the minimum and maximum values of the area are.

Another way is $f(x+ e) \approx f(x) + e f'(x)$ is e is small. (e is the error)

4. Mar 8, 2010

### steve snash

Re: how do you find the approximate uncertainty of a circle of radius 3.8x10^4????

thanks willem, saved my life =)