To find the length of the hypotenuse \( c \) of a right triangle, we use the Pythagorean theorem:
\[
a^2 + b^2 = c^2,
\]
where \( a \) and \( b \) are the lengths of the legs, and \( c \) is the hypotenuse.
We are given that:
\[
a = 8
\text{and}
b = 15.
\]
Substitute these values into the Pythagorean theorem:
\[
8^2 + 15^2 = c^2.
\]
Now, square the values of \( a \) and \( b \):
\[
64 + 225 = c^2.
\]
Add the results:
\[
289 = c^2.
\]
Now, take the square root of both sides:
\[
c = \sqrt{289} = 17.
\]
Thus, the length of the hypotenuse is \( c = 17 \).