Answer :
The hypotenuse is given by the Pythagorean theorem:
[tex]c=\sqrt{a^2+b^2}[/tex]
Since a=b-5, the expression becomes
[tex]c=\sqrt{(b-5)^2+b^2}[/tex]
Expand the square
[tex]c=\sqrt{b^2-10b+25+b^2}=\sqrt{2b^2-10b+25}[/tex]
Unless you're given an explicit value for b, that's all we can say.