A sketch of the cinema screen is 72 metres long and 54 metres wide.

What is the diagonal length of the screen?

Let the diagonal be a.

now, as we know that each angle in a rectangle is right angle.

thus we have a right angled triangle.

now, we can apply pythagoras theorum.

a^2 = 54^2 + 72^2

= 2916 + 5184

=8100

thus, a^2 = 8100

thus, a = 90.

Thus the diagonal is 90metres