Diagonal of a rectangle formula:
Diagonal = √l² + w²
Diagonal = √10² + 8²
Diagonal = √100 + 64
Diagonal = √164
Diagonal = 12.806 feet.
Or you can use the pythagorean theorem. The diagonal of a rectangle is the hypotenuse of a triangle.
a² + b² = c² ; where a and b represents the lengths of the triangle and c is the hypothenuse. In this case, the lengths are 10 ft and 8ft.
10² + 8² = 100 + 64 = 164 ; This represents c².
c = √c² = √164 = 12.806 ft