# Area of a Rectangle by the length of one side and the diagonal

This online calculator finds the area of a rectangle from the length of one side and the diagonal.

Rectangle is a quadrilateral having opposing sides parallel and four right angles. To find the area of a rectangle you should multiply its length by its width. The equation is

However, you may know only the length of one side and the diagonal. It this case you first should use the Pythagorean theorem to find the another side. If *a* and *b* are the sides, and *d* is the diagonal, the Pythagorean theorem states that

From there

and the final formula for the area of a rectangle is

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