Question 1013656
Since diagonals of a rhombus meet at right angles, you have 4 right triangles with the sides being the hypotenuses...the legs are 10 and x with the hypotenuse being 26...draw it and see...
Anyway, the missing half-diagonal is found by
10^2 + x^2 = 26^2
x = 24
so that the whole missing diagonal is 48 cm.