Elementary Geometry for College Students (7th Edition)

As we know the diagonals of a rhombus equally divides each other at $90^{\circ}$. So the distance of the congruent sides is the hypotenuse of the right triangle formed by the diagonals of the rhombus . The two sides of the triangle are half of the diagonals means 3 and 4. $Hypotenuse^{2}= 3^{2}+4^{2}$ Hypotenuse = 5 So the distance of the congruent sides = 5.