jmc

The length of the hypotenuse is given by the distance formula to be $\sqrt{(5-(-1){)}^2+(-5-(-1){)}^2}=\sqrt{6^2+4^2}=\sqrt{52}$. The length of the leg is then given by $\sqrt{52}/\sqrt{2}=\sqrt{26}$ (alternatively, the Pythagorean Theorem can be applied), and the area of the isosceles right triangle is then equal to $\frac{1}{2}\cdot \sqrt{26}\cdot \sqrt{26}=\boxed{13}.$