Question Number 18463 by Tinkutara last updated on 22/Jul/17
$$\mathrm{The}\:\mathrm{solid}\:\mathrm{angle}\:\mathrm{subtended}\:\mathrm{by}\:\mathrm{a}\:\mathrm{spherical} \\ $$$$\mathrm{surface}\:\mathrm{of}\:\mathrm{radius}\:{R}\:\mathrm{at}\:\mathrm{its}\:\mathrm{centre}\:\mathrm{is}\:\frac{\pi}{\mathrm{2}} \\ $$$$\mathrm{steradian},\:\mathrm{then}\:\mathrm{the}\:\mathrm{surface}\:\mathrm{area}\:\mathrm{of} \\ $$$$\mathrm{corresponding}\:\mathrm{spherical}\:\mathrm{section}\:\mathrm{is} \\ $$
Answered by ajfour last updated on 22/Jul/17
$$\mathrm{S}=\mathrm{R}^{\mathrm{2}} \theta_{\mathrm{s}} =\frac{\pi}{\mathrm{2}}\mathrm{R}^{\mathrm{2}} . \\ $$
Commented by Tinkutara last updated on 22/Jul/17
$$\mathrm{Thanks}\:\mathrm{Sir}! \\ $$