In fig, ∠B < ∠A and ∠C < ∠D. Show that AD < BC.

It is given that ∠B < ∠A and ∠C < ∠D.
We know that the side opposite to a larger angle is larger.
OD < OC (i)
AO < BO (ii)
Adding eq(i) and eqn (ii), we get
AO + OD < BO + OC
→ AD < BC [hence proved]