The surface area of a cube is 13.5 m². What is the length (in m) of its diagonal ?

$1.5 \sqrt{3}$

We know that,

Surface area of a cube = 6(side)²

Diagonal of cube = \(\sqrt {3}\) × Side of cube

We have,

The surface area of the cube = 13.5 m²

According to the question,

6 × side² = 13.5 

side = 1.5 

Longest diagonal = \(\sqrt {3}\) × Side of cube = 1.5\(\sqrt {3}\)