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ABC is a traingle right angled …

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ABC is a traingle right angled at B and BD perpendicular to AC. If AD=4 cm and CD=5 cm. Then find BD and AB.
  • 2 answers

Aditi Ringusia 4 years, 8 months ago

Sir please can u explain how it is 90degree - angle c

Gaurav Seth 4 years, 8 months ago

Given,

∆ABC in which ∠B = 90° and BD ⊥ AC

 

Also, AD = 4 cm and CD = 5 cm

 

In ∆ADB and ∆CDB,

 

∠ADB = ∠CDB [each equal 90°]

 

∠BAD = ∠DBC [each equal to 90°-∠C]

 

∴ ∆DBA ∼ ∆DCB [by AAA similarity criteria]

 

Then,

In right angled ∆BDC,

 

BC2 = BD2 + CD2 [by Pythagoras theorem]

 

= BC2 = (2√5)2 + (5)2

 

= BC2 = 20 + 25 = 45

 

= BC = √45 = 3√5

 

Again,

Hence, BD = 2√5cm and AB = 6cm.

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