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Mathematics

In the given figure, AD = BD, then angle ACD is :

  1. 43°

  2. 22°

  3. 65°

  4. 28°

In the given figure, AD = BD, then angle ACD is : Isosceles Triangles, Concise Mathematics Solutions ICSE Class 9.

Triangles

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Answer

Given,

AD = BD

In △ ABD,

⇒ ∠BAD = ∠ABD = 65° (Angles opposite to equal sides are equal)

In △ ABC,

⇒ ∠BAC = ∠BAD + ∠DAC = 65° + 22° = 87°.

By angle sum property of triangle,

⇒ ∠BAC + ∠ACB + ∠CBA = 180°

⇒ 87° + ∠ACB + 65° = 180°

⇒ ∠ACB + 152° = 180°

⇒ ∠ACB = 180° - 152° = 28°.

From figure,

⇒ ∠ACD = ∠ACB = 28°.

Hence, Option 4 is the correct option.

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