The diagonal of a rectangle is measured by using Pythagores theorem if you have the length and breadth of the rectangle. Say the length is 4cm and breadth is 3cm then the diagonal(hypotenuse) would be 42 + 32 =16 + 9= 25 = 52. Hence the hypotenuse or the diagonal is 5cm. Is that fine? Have a good day.

Diagonal lines are used for many things like art and designs. They can be used for buildings.

Diagonal = 18*sqrt(2) = 18*1.414214 = 25.45584 feet

Plant slant.

The diagonal of a square whose area is 36 is the square root of 72, or about 8.49. Since the area of a square is side(squared), then the sides are each 6. Then since a(squared) + b(squared) = c(squared), for a triangle (the diagonal), you get the square root of 72.