Given: In figure, ∠B < ∠A and ∠C < ∠D.
To Prove: AD < BC
Proof: ∠B < ∠A | Given
∴ ∠A > ∠B
∴ OB > OA ...(1)
| Side opposite to greater angle is longer
∠C < ∠D | Given
∴ ∠D > ∠C
∴ OC > OD ...(2)
| Side opposite to greater angle is longer
From (1) and (2), we get
OB + OC > OA + OD
⇒ BC > AD
⇒ AD < BC.
[Hint. Produce AD to E such that AD = DE and join C and E.]
OR
Prove that the sum of any two sides of a triangle is greater than twice the length of median drawn to the third side.
Prove that the sum of the three sides of a triangle is greater than the sum of its three medians.
OR
Prove that the perimeter of a triangle is greater than the sum of its three medians.