Given:In Δ ABC, ∠A = 100°, AD bisects ∠A and AD ⊥ BCFormula Used/Theory:-Pythagoras theorem:-Base2 + Height2 = Hypotenuse2When ∠A is bisectedThen;∠DAB = 50° and ∠DAC = 50°Then;In Δ ABDAs AD ⊥ BC∠ADB = 90°Sum of all angles is 180°∠ADB + ∠DAB + ∠B = 180°90° + 50° + ∠B = 180°∴ ∠B = 180° - 140° = 40°

Q. 405.0( 3 Votes )

In Δ ABC, <span l A. 80°

B. 20°

C. 40°

D. 30°

Class 7th NCERT - Exemplar Mathematics 6. Triangles

Answer :

Given:

In Δ ABC, ∠A = 100°, AD bisects ∠A and AD ⊥ BC

Formula Used/Theory:-

Pythagoras theorem:-

Base² + Height² = Hypotenuse²

When ∠A is bisected

Then;

∠DAB = 50° and ∠DAC = 50°

Then;

In Δ ABD

As AD ⊥ BC

∠ADB = 90°

Sum of all angles is 180°

∠ADB + ∠DAB + ∠B = 180°

90° + 50° + ∠B = 180°

∴ ∠B = 180° - 140° = 40°

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PREVIOUSIn Fig. 6.16, if NEXTIn ∆ABC, <span la

In Δ ABC, <span l A. 80°B. 20°C. 40°D. 30°

In Δ ABC, <span l A. 80°

B. 20°

C. 40°

D. 30°