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In △ABC, ∠B = 35°, ∠C = 65° and the bisector AD of ∠BAC meets BC at D. Arrange the sides AD, BD and CD in ascending order of their lengths.

In △ABC, ∠B = 35°, ∠C = 65° and the bisector AD of ∠BAC meets BC at D. Arrange the sides AD, BD and CD in ascending order of their lengths. R.S. Aggarwal Mathematics Solutions ICSE Class 9.

Triangles

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Answer

In △ADB,

⇒ ∠BAD + ∠ADB + ∠ABD = 180°

⇒ 40° + ∠ADB + 35° = 180°

⇒ ∠ADB + 75° = 180°

⇒ ∠ADB = 180° - 75°

⇒ ∠ADB = 105°.

We know that,

The shortest side of a triangle has the smallest angle opposite to it.

In triangle ABD,

Since,

⇒ ∠B < ∠A

⇒ AD < BD …….(1)

From figure,

∠ADB + ∠ADC = 180° (Linear pair)

⇒ ∠ADC + 105° = 180°

⇒ ∠ADC = 180° - 105°

⇒ ∠ADC = 75°

In triangle ACD,

Since,

⇒ ∠A < ∠C

⇒ CD < AD ……..(2)

From eq.(1) and (2) we have:

⇒ CD < AD < BD

Hence, CD < AD < BD.

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