How can we find the radius of cylinder

Volume of a cylinder: V = π * r² * h,
Base surface area of a cylinder: A_b = 2 * π * r²,
Lateral surface area of a cylinder: A_l = 2 * π * r * h,
Total surface area of a cylinder: A = A_b + A_l,
Longest diagonal of a cylinder: d² = 4 * r² + h²,
Surface-area-to-volume ratio of a cylinder: SA:V = A / V = 2 * (r + h) / (r * h)

21/2 or 5/2

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.