In a right triangle, the two sides that form the right angle are called the legs, and the side opposite the right angle is called the hypotenuse.
For a right triangle with legs of lengths 4 and 5, you can calculate the length of the hypotenuse \( c \) using the Pythagorean theorem, which states:
\[ c^2 = a^2 + b^2 \]
where \( a \) and \( b \) are the lengths of the legs. Substituting the values:
\[ c^2 = 4^2 + 5^2 \] \[ c^2 = 16 + 25 \] \[ c^2 = 41 \] \[ c = \sqrt{41} \approx 6.403 \]
So, the hypotenuse of the right triangle is approximately 6.403 units long.