Respuesta :
recall that a Unit Circle is called that because its radius is just 1.
now, using the pythagorean theorem, c = √( a² + b²) whatever the values for "a" and "b" in the (a,b) point, they must yield a value c = 1, a radius of 1.
[tex]\bf \boxed{A}~\hspace{5em}c=\sqrt{\left( \frac{6}{7} \right)^2+\left( \frac{\sqrt{13}}{7} \right)^2}\implies c=\sqrt{\frac{36}{49}+\frac{13}{49}}\implies c=\sqrt{\frac{49}{49}} \\\\\\ ~\hspace{7em}c=\sqrt{1}\implies c=1~~\textit{\Large \checkmark} \\\\\\ \boxed{B}~\hspace{5em}c=\sqrt{\left( \frac{5}{13} \right)^2+\left( \frac{12}{13} \right)^2}\implies c=\sqrt{\frac{25}{169}+\frac{144}{169}}\implies c=\sqrt{\frac{169}{169}} \\\\\\ ~\hspace{7em}c=\sqrt{1}\implies c=1~~\textit{\Large \checkmark}[/tex]
