Prove that the sum of any two sides of a triangle is greater than twice the median concerning the third side.
Given: ABC is a triangle
AD is the median at BC drawn from A.
Produce D to E and DE = AD, Join DE
To Prove: AB + AC > AD
Proof: Let ABD and ECD
CD = DB (D is mid-point)
BDA = CDE (Vertically opposite angle)
ED = AD (by construction)
ABD ECD (by SAS congruence)
Þ EC = AB (by CPCT)
In ACE, AC + EC > AE (Sum of two sides is greater than the third side)
Then AC + AB > AD + DE (QAB = EC and AE = AD + DE as D is the mid-point)
AC + AB > 2AD
AC + AB > AD
Hence proved.