1.

In the given figure, ∠ACB = 90° CD ⊥ AB  Prove that BC2/AC2 = BD/AD

Answer»

Given: ∠ACB = 90° And CD⊥AB

To Prove; BC2/AC2 = BD/AD

Proof: In ∆ ACB and ∆ CDB 

∠ACB = ∠COB = 90° (Given) 

∠ = ∠ (Common) 

By AA similarity-criterion ∆ ACB ~ ∆CDB 

When two triangles are similar, then the ratios of the lengths of their corresponding sides are proportional. 

∴ BC/BD = AB/BC 

⇒ BC2 = BD. AB … (1) 

In ∆ ACB and ∆ ADC 

∠ACB = ∠ADC = 90° (Given) 

∠CAB = ∠DAC (Common) 

By AA similarity-criterion ∆ ACB ~ ∆ADC

When two triangles are similar, then the ratios of their corresponding sides are proportional.

∴ AC/AD = AB/AC 

⇒ AC2 = AD. AB ….(2) 

Dividing (2) by (1), we get 

BC2/AC2 = BD/AD



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