see the picture attached to better understand the problem
we know that
in the right triangle ABC
AB is equal to AC
[tex] AB=AC=6units [/tex]
BC is the hypotenuse
Applying the Pythagorean Theorem
[tex] BC^{2} =AB^{2}+AC^{2}\\ BC^{2} =6^{2} +6^{2} \\ BC^{2} =72\\ BC=\sqrt{72} \\ BC=6\sqrt{2} units [/tex]
therefore
the answer is
the length of the hypotenuse is [tex] 6\sqrt{2} [/tex] units