jmc

Square each side length to obtain $2u-1$, $2u+1$, and $4u$. Notice that the first two expressions, $2u-1$, $2u+1$, sum to give the third. Therefore, the sides of the triangle satisfy the Pythagorean theorem, and the triangle is a right triangle. The measure of the largest angle in a right triangle is $\boxed{90}$ degrees.