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May 5th, 2015, 12:12 PM   #1
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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.
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May 5th, 2015, 12:23 PM   #2
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$\displaystyle A = \frac{\theta}{2} r^2$

$\displaystyle A = (0.4)(400 \, mm)^2 = 64000 \, mm^2$

$\displaystyle A = (0.4)(0.4 \, m)^2 = 0.064 \, m^2$

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.
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May 5th, 2015, 12:42 PM   #3
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So it is... :/

Had bit of a dull moment.
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