Question 273121
Rectangle is 3ft wide and 4ft long, we have a right-angled triangle which should be well known (3-4-5).


The hypotenuse (by Pythagoras) is the square root of the sum of the squares of the other two sides:


3x3 + 4x4 = 9 + 16 = 25


Therefore the hypotenuse is 5ft.


The diagonal (which is the hypotenuse) is 5ft long.