Solve for r
r=4\sqrt{5}\approx 8.94427191
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4\sqrt{5}=r
Factor 80=4^{2}\times 5. Rewrite the square root of the product \sqrt{4^{2}\times 5} as the product of square roots \sqrt{4^{2}}\sqrt{5}. Take the square root of 4^{2}.
r=4\sqrt{5}
Swap sides so that all variable terms are on the left hand side.
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