Step-by-step explanation:
1)
In a right triangle longest side is hypotenuse and the remaining two sides represent the perpendicular legs.
Hence, from the given question it is obvious that 25 is hypotenuse and 20 and 15 are perpendicular legs.
Now, by Pythagorean theorem:
2)
Because all right triangles have one hypotenuse and two perpendicular legs.