In figure, if ∠BAC = 90° and AD ⊥ BC. Then,
In ∆ADB and ∆ADC,
It is given that,
∠D = ∠D = 90° (∵ AD ⊥ BC)
∠DBA = ∠DAC [each angle equals to 90°- <C]
Now by AAA similarity criteria,
∆ADB ∼ ∆ADC
→ BD/AD = AD/CD
→ BD.CD = AD �