Answer :

Use the pethagorem theorem!
[tex]a^{2} + b^{2} =c^{2} [/tex]
in this case, a will be 9, b will be 1(it can be a is 1 and b is 9), and solve for c.
[tex]9^{2}+1^{2}=c^{2}[/tex]
[tex]81+1=c^{2}[/tex]
[tex] \sqrt{82} =c[/tex]