- #1

JustynSC

- 17

- 0

## Homework Statement

What is the area, and approximate uncertainty in a circle with radius 3.1*10^4 cm (or written: 3.1e4 cm)?

## Homework Equations

Area=Pi*r^2

## The Attempt at a Solution

My attempt to the solution took some trial and error, and it went as follows:

Substitute the circle's radius into the equation for the area of the circle: A=Pi(3.1e4)^2

Then I squared the () : A=Pi(9.61e8)

Following this I Multiplied by Pi: 3.017e9 cm^2 (sig fig) ==> 3.0e9 cm^2

This answer above Is correct, but in the book the answer is 3.0+/-0.2e9 cm^2.

The part that I do not understand is that the uncertainty they predict is +/-0.2

I figured that the uncertainty should be +/- 0.1e4, giving the radius a minimum of 3.0e4, and a max of 3.2e4.

Based on my way of working though the problem, my answer come out to be A=3.0+/-0.1e9 cm^2

If anyone can explain why my uncertainty isn't correct, and how they get that answer that would be wonderful!