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Mathematics

Statement (1): In the given figure, AC = DC = BD and ∠B = 30°.

Statement 1 - In the given figure, AC = DC = BD and ∠B = 30°. Statement 2 - ΔCAD is equilateral. Isosceles Triangles, Concise Mathematics Solutions ICSE Class 9.

Statement (2): ΔCAD is equilateral.

  1. Both the statements are true.

  2. Both the statements are false.

  3. Statement 1 is true, and statement 2 is false.

  4. Statement 1 is false, and statement 2 is true.

Triangles

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Answer

In ΔBDC,

⇒ DC = DB

⇒ ∠DBC = ∠DCB = 30° (Angles opposite to equal sides of a triangle are always equal)

In ΔBDC, according to angle sum property,

⇒ ∠BDC + ∠DBC + ∠DCB = 180°

⇒ ∠BDC + 30° + 30° = 180°

⇒ ∠BDC + 60° = 180°

⇒ ∠BDC = 180° - 60°

⇒ ∠BDC = 120°

Since ∠BDC and ∠CDA forms linear pair.

⇒ ∠BDC + ∠CDA = 180°

⇒ 120° + ∠CDA = 180°

⇒ ∠CDA = 180° - 120°

⇒ ∠CDA = 60°

Since, AC = DC

⇒ ∠CDA = ∠CAD = 60° (Angles opposite to equal sides of a triangle is always equal)

In ΔACD, according to angle sum property,

⇒ ∠ACD + ∠CDA + ∠CAD = 180°

⇒ ∠ACD + 60° + 60° = 180°

⇒ ∠ACD + 120° = 180°

⇒ ∠ACD = 180° - 120°

⇒ ∠ACD = 60°

So, ΔCAD is equilateral.

∴ Both the statements are true.

Hence, option 1 is the correct option.

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