Solve for r
r = \frac{100}{\pi} \approx 31.830988618
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2\pi r=200
Swap sides so that all variable terms are on the left hand side.
\frac{2\pi r}{2\pi }=\frac{200}{2\pi }
Divide both sides by 2\pi .
r=\frac{200}{2\pi }
Dividing by 2\pi undoes the multiplication by 2\pi .
r=\frac{100}{\pi }
Divide 200 by 2\pi .
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