Given:
The length of the book is 24 inches.
The width of the book is 21 inches.
To find:
The length of the hypotenuse
Step-by-step explanation:
Using the Pythagoras theorem,

On substitution, we get

Thus, the length of the hypotenuse side is 31.89 inches.
The hypotenuse that measures with a ruler equals the hypotenuse.
Yes, the both are same always.
Final answer:
The length of the hypotenuse side is 31.89 inches.