SOLUTION: The diagonal of a rohmbus are 30 cms and 40 cm long.find its side.

In any rhombus, the diagonals bisect each other and are perpendicular.

It is the characteristic property of a rhombus.


Therefore, the diagonals of a rhombus divide it in four congruent right-angled triangles.


For each of these triangles, the halves of diagonals are the legs, while the side of a rhombus is the hypotenuse of such a triangle.


So, you have right angled triangle with the legs  = 15 cm  and   = 20 cm.


Hence, the side of the rhombus, which is the hypotenuse of the right angled triangle, is  =  =  = 25 cm long.


Answer.  The side of the rhombus is 25 cm long.