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# Calculate Diagonal

## Calculate the diagonal of a rectangle or square

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Enter the length and width of the rectangle:

## Calculating the diagonal of a rectangle

Calculating the diagonal of a rectangle is a fundamental application of the Pythagorean theorem. The Pythagorean theorem states that in a right triangle (a triangle where one of the angles is 90 degrees), the square of the length of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the lengths of the other two sides.

In the case of a rectangle, the two sides are the length and width of the rectangle, and the diagonal acts as the hypotenuse. So if we denote the length of the rectangle as 'a' and the width as 'b', then the length of the diagonal 'd' is given by the formula:

`d = √(a² + b²)`

In this formula, the square of the length and width of the rectangle is added together and the square root of that sum is taken to find the length of the diagonal.

This way, if you know the length and width of a rectangle, you can easily calculate the length of its diagonal. This is a useful calculation in many fields, including construction, design, and even navigation.