Final answer:
The side across from the right angle in a right triangle is known as the hypotenuse, which can be calculated using the formula c = √(a² + b²) from the Pythagorean theorem.
Step-by-step explanation:
The side across from the right angle in a right triangle, stretching from one leg to the other, is called the hypotenuse. This is the longest side of the right triangle and is opposite the right angle.
According to the Pythagorean theorem, the relationship between the lengths of the legs (labeled a and b) and the hypotenuse (labeled c) is expressed as a² + b² = c². The length of the hypotenuse can therefore be calculated using the formula c = √(a² + b²), where √ denotes the square root.