Question Number 13373 by Stargazer last updated on 19/May/17
Commented by Stargazer last updated on 19/May/17
$${find}\:{the}\:{area}\:{of}\:{the}\:{ring}? \\ $$
Commented by prakash jain last updated on 20/May/17
$$\mathrm{Inner}\:\mathrm{circle}\:\mathrm{radius}\:\mathrm{is}\:{r}\mathrm{sin}\:\theta. \\ $$$$\mathrm{Width}\:\mathrm{of}\:\mathrm{ring}\:\mathrm{is}\:\mathrm{not}\:\mathrm{clear}\:\mathrm{from} \\ $$$$\mathrm{the}\:\mathrm{picture} \\ $$
Commented by Stargazer last updated on 20/May/17
$${its}\:{rd}\theta \\ $$
Commented by prakash jain last updated on 20/May/17
$$\pi\left({r}\mathrm{sin}\:\theta+{rd}\theta\right)^{\mathrm{2}} −\pi\left({r}\mathrm{sin}\:\theta\right)^{\mathrm{2}} \\ $$$$=\pi{r}^{\mathrm{2}} \left(\mathrm{2sin}\:\theta{d}\theta+\left({d}\theta\right)^{\mathrm{2}} \right) \\ $$