Question

Help me solve this please!!!!!

Answer 1

`s = 4\pi {r}^(2) \\ (ds)/(dr) = 8\pi r =8\pi(2) = 16\pi \\ from \: chain \: rule \\ (ds)/(dr) = (ds)/(dt) . (dt)/(dr) \\ but \: (ds)/(dt) = 1 \\ 16\pi = 1 * (dt)/(dr) \\ (dt)/(dr) = 16\pi \\ (dr)/(dt) = ( (dt)/(dr) ) ^( - 1) \\ (dr)/(dt) = (1)/(16\pi)`