1.

In ∆ABC if AB = AC and a point D lies of AC such that BC2 = AC × DC, then Prove that BD = BC.

Answer»

Given : In ∆ABC, AB = AC and BC2 = AC × DC,

where D is any point on side AC.

To prove : BD = BC

Proof : Given that BC2 = AC × DC

⇒ BC/DC = AC/BC …..(i)

Now in ∆ABC and ∆BDC

∠C = ∠C (common angle)

and BC/DC = AC/BC [from (i)]

Thus, by SAS similarity criterion

∆ABC ~ ∆BDC

⇒ AC/BC = AB/BD …..(ii)

Given, AB = AC

Thus, AC/BC = AC/BD

⇒ BC = BD.



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