Because that is the accepted convention. The hypotenuse is the longest side of a right triangle, the side opposite the right angle. The term comes from the Greek, hypoteinousa, meaning "to stretch", and was used by Plato in the Timeus 54d and by other ancient authors. For more information, please see the Related Link below.
The side opposite the right angle is called the hypotenuse.
The Hypotenuse
It is called the hypotenuse
The longest side of a right-angled triangle is always opposite the right-angle and is called the hypotenuse.
The hypotenuse.
The hypotenuse is the longest side of a right angle triangle and it is opposite the 90 degree right angle.
The Hypotenuse of the opposite of the Right Angle
The side opposite the right angle is called the hypotenuse
The side opposite the right angle of a right angle triangle is the hypotenuse
It is the hypotenuse
The side opposite the right angle of a triangle is the hypotenuse which is the longest side
adjacent, opposite and hypotenuse