Question

Side of cube is 7cm then find the diagonal of cube is?

Answer 1

Since all faces of a cube are right angled, to adjacent ones.

We apply Pythagorean-Theorem to find lengths of hypotenuse.

First, diagonals in each faces are equal to :

$l^2=a^2+a^2$ → $l=\sqrt{2} a$

Then, diagonals in a cube will equal to :

$l^2=2a^2+a^2$ → $l=\sqrt{3} a$

The diagonal of a cube is √3 times the edge.

Now you can do it yourself. If it's hard then draw a 3D picture in your head. It will definitely help you understand. Hope it helps.