In a right triangle with a 45-degree angle, the two legs are of equal length, and the relationship between the length of a leg and the hypotenuse \( c \) is given by:
\[ c = \text{leg} \times \sqrt{2} \]
For the second triangle, we are given that the side opposite the 45-degree angle is \( 4\sqrt{2} \). Since this is a 45-45-90 triangle, both legs are equal. Therefore, both legs have a length of \( 4\sqrt{2} \).
Now, using the formula for the hypotenuse:
\[ c = 4\sqrt{2} \times \sqrt{2} = 4 \times 2 = 8 \]
Thus, the length of the hypotenuse in the second triangle is 8.
Therefore, the correct answer is: the hypotenuse of the second triangle has length 8.