In the given Fig, ABC is a right triangle, right angled at B. AD and CE are two medians drawn from A and C respectively. If AC = 5 cm and find the length of CE.
Const: Draw AE ⊥ BC
Proof : In ∆ABE and ∆ACE, we have
AB = AC [given]
AE = AE [common]
and ∠AEB = ∠AEC [90°]
Therefore, by using RH congruent condition
∆ABE ~ ∆ACE
⇒ BE = CE
In right triangle ABE.
AB2 = AE2 + BE2 ...(i)
[Using Pythagoras theorem]
In right triangle ADE,
AD2 = AE2 + DE2
[Using Pythagoras theorem]
Subtracting (ii) from (i), we get
AB2 - AD2 = (AE2 + BE2) - (AE2 + DE2)
AB2 - AD2 = AE2 + BE2 - AE2 - DE2
⇒ AB2 - AD2 = BE2 - DE2
⇒ AB2 - AD2 (BE + DE) (BE - DE)
But BE = CE [Proved above]
⇒ AB2 - AD2 = (CE + DE) (BE - DE)
= CD.BD
⇒ AB2 - AD2 = BD.CD Hence Proved.