Solve for r
r=\frac{2}{\pi }\approx 0.636619772
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2\pi r=4
The equation is in standard form.
\frac{2\pi r}{2\pi }=\frac{4}{2\pi }
Divide both sides by 2\pi .
r=\frac{4}{2\pi }
Dividing by 2\pi undoes the multiplication by 2\pi .
r=\frac{2}{\pi }
Divide 4 by 2\pi .
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