In the figure given below, ABCD is a square and DEC is an equilateral triangle. The points A and E are joined by a straight line.

F1 Madhuri UPSC 11.01.2023 D1

Then, ∠DAE equals

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45th BPSC Prelims (Held in 2002) Official paper
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  1. 15°
  2. 10°
  3. 30°
  4. 20°

Answer (Detailed Solution Below)

Option 1 : 15°
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Detailed Solution

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The correct answer is option 1.

Given:  ABCD is a square and DEC is an equilateral triangle. Points A and E are joined by a straight line.

Calculation:

⇒ ABCD is a square, then ∠ADC = 90°

AB=BC=CD=DA

⇒ DCE is an equilateral triangle, then ∠EDC = 60°

DC=DC=CE

⇒ Hence, AB=BC=CD=DA=CE=DC

F1 Madhuri UPSC 11.01.2023 D1

⇒ Now, In △ADE,

AD=DE

⇒ If two sides are equal , then the two angles opposite to the equal sides will also be equal.

⇒ Thus, ∠AED=∠DAE=x°

∠ADE=∠ADC+∠EDC

∠ADE=90°+60°

∠ADE=150°

Sum of angles of triangle ADE = 180

∠ADE+∠AED+∠DAE=180

150+x+x=180

⇒ x=15° 

Hence, ∠DAE=15°

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