Video narration
Can you find a notebook's diagonal from its length and width without measuring it? Draw the diagonal, and the rectangle becomes a right-angled triangle. The diagonal is not just a line across the notebook; it becomes the hypotenuse: the side opposite the 90-degree angle, and the longest side. The two notebook edges meeting at the corner are the other sides, called a and b. Now Pythagoras' theorem connects them: a2 + b2 = c2, where c is the hypotenuse. To find an unknown diagonal, square the length and width, add them, and take the positive square root: c = √(a2 + b2). Keep both lengths in the same unit. This rule works only for a triangle with a right angle, not an arbitrary triangle. So yes-your notebook's diagonal can be calculated: diagonal2 = length2 + width2; take the square root, and you have the answer.