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May 5th, 2015, 12:12 PM  #1 
Newbie Joined: Dec 2014 From: uk Posts: 10 Thanks: 0  Calculating area in circle question..
Ok... Here's my question, when calculating an area of a circle im getting totally different sizes by using different length types. Eg. A circle wih a radius of 400mm and an angle of 0.8 rad is showing up totally different results to a circle with a radius of 0.4m and an angle f 0.8 rad... After working it out and converting the results they differ. What am I missing here. 
May 5th, 2015, 12:23 PM  #2 
Math Team Joined: Jul 2011 From: Texas Posts: 2,949 Thanks: 1555 
$\displaystyle A = \frac{\theta}{2} r^2$ $\displaystyle A = (0.4)(400 \, mm)^2 = 64000 \, mm^2$ $\displaystyle A = (0.4)(0.4 \, m)^2 = 0.064 \, m^2$ note ... $\displaystyle 1 \, m^2 = 10^6 \, mm^2$ so ... $\displaystyle 0.064 \, m^2 \times 10^6 \, mm^2/m^2 = 64000 \, mm^2$ same same. 
May 5th, 2015, 12:42 PM  #3 
Newbie Joined: Dec 2014 From: uk Posts: 10 Thanks: 0 
So it is... :/ Had bit of a dull moment. 

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area, calculating, circle, question 
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