[tex]\begin{gathered} \text{The point }(4,7)\text{ represents a }(x,y)\text{ coordinate thus, we can substitute the values to the} \\ \text{equation of the circle},\text{ to solve for radius }r \\ (x-1)^2+(y-3)^2=r^2 \\ (4-1)^2+(7-3)^2=r^2 \\ (3)^2+(4)^2=r^2 \\ 9+16=r^2 \\ 25=r^2 \\ \sqrt[]{25}=\sqrt[]{r^2} \\ r=5 \\ \text{Therefore, the length of the radius of circle A is }5\text{ units.} \end{gathered}[/tex]
