Let a, b, c be the sides of triangle A B C such that 2 b=a+c. If \frac{2 !}{1 ! 9 !}+\frac{2 !}{3 ! 7 !}+\frac{1 !}{5 ! 5 !}=\frac{8^{a}}{(2 c) !}, then

circumradius of \triangle {ABC} is 5

inradius of \triangle {ABC} is 1

\triangle {ABC} is right angled triangle