A=v^2/r solve for v, solve for r

To rearrange these for v and r we must use BEDMAS.

First, times both sides by r, getting Ar = v²r/r
You can cancel out r/r to get Ar = v²

To get v, square root both sides. √Ar = √v²
Cancel out the square root and the squared v = √Ar

To get r, go back to Ar = v², then divide both sides by A. rA/A = v²/A
Then cancel out A/A to get r. r = v²/A

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