What is the length of a diagonal of a cube with a side length of 10 cm?

Well, since it is a cube, we know the length of all the sides of 10 cm, so we can create a triangle using the sides of a square and use pythagorean theorem

A²+B²=C²

C being the hypotenuse, or the diagonal we are looking for, so 10²+10² = 200

Then we square root to find C, so √200 = 14.14213562