In Δ ABC =  ∠A = 2∠B. The bisector of ∠A meets BC at D such that CD = 4 cm and BD = 6 cm. The length of side AC is:

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AAI Junior Assistant (Fire Service) Official Paper (Held On: 15 Nov, 2022 Shift 2)
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  1. cm 
  2.  cm 
  3.  cm 
  4.  cm

Answer (Detailed Solution Below)

Option 2 :  cm 
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ST 1: English
20 Qs. 20 Marks 25 Mins

Detailed Solution

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Given:

ΔABC, ∠A = 2∠B

AD bisects ∠A

CD = 4 cm

BD = 6 cm

Image of triangle ABC

Formula used:

Congruent triangles: Corresponding sides and angles are equal.

Calculation:

DC = 4 cm 

BC = 6 + 4 = 10 CM

Now in Δ ACB and Δ DCA

ΔACB, ∠A = 2∠B = 2X

∠BAC = 2X, ∠ABC = X

And, Now in Δ DCB

ADC = 2X (Sum of interior angle is equal to opposite exterior angle.)

∠DAC = X (As AD is bisector of ∠A)

And AC is common in both the triangle.

Then by ASA(angle side angle) Δ ACB and Δ DCA is congruent. 

Then, 

AC/DC = CB/CA

AC2 = DC × CB

AC2 = 4 × 10

AC = 2√10

∴ The length of side AC is 2√10 cm.

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