Respuesta :

The diagonal of length 2r forms the hypotenuse of a right angled triangle with  one leg ( the width of the rectangle) = x. So by Pythagoras:-

(2r)^2 = h^2 + x^2      where h = height of the rectangle

h^2 = 4r^2 - x^2

h =  √ (4r^2 - x^2)     answer