Answer: A; r = square root (S/4pi)
Step-by-step explanation:
1. Divide 4pi on both sides to get r^2 by itself so the left side becomes S/4pi (you do this because 4, pi, and r^2 are being multiplied together on the right side in the original equation so to cancel that out and get r by itself you do the opposite of multiplication)
The equation should now look like r^2 = S/4pi
2. Square root both sides including r to get rid of the r^2 so it becomes just r (also when you square root both sides, you square root all of S/4pi not just S or 4pi but the whole thing)
After you do that, you get r = square root (S/4pi) which is answer A
Hope this helps! :)
