Question

please solve this with steps .its emergency

Answer 1

Let the diagonals intersect at point O.
triangle AOB is similar to triangle COD by using AA.
angle AOB= COD(vertically opp. angles)
angle OAB=OCD(alternate interior angles) 
Therefore ratio of corresponding sides is equal.
AO/OC=AB/CD

1/2=AB/CD (CD>AB)
therefore
CD=2AB