Question Number 40867 by ajfour last updated on 28/Jul/18
Commented by MrW3 last updated on 28/Jul/18
$${as}\:{shown}\:\mathrm{sin}\:\frac{\theta}{\mathrm{2}}=\frac{{a}}{\mathrm{2}{R}} \\ $$$$\Rightarrow\theta=\mathrm{2}\:\mathrm{sin}^{−\mathrm{1}} \frac{{a}}{\mathrm{2}{R}} \\ $$$${but}\:{I}\:{think}\:{you}\:{meant}\:{something} \\ $$$${others}. \\ $$