What is the value of sin 75° + sin 15°?

This question was previously asked in
SSC CGL 2022 Tier-I Official Paper (Held On : 09 Dec 2022 Shift 4)
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Answer (Detailed Solution Below)

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PYST 1: SSC CGL - General Awareness (Held On : 20 April 2022 Shift 2)
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Detailed Solution

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Given:

sin 75° + sin 15°

Concept used:

1. 2 × sin θ × cos θ = sin 2θ

2. sin (90° - θ) = cos θ

3. sin 30° = 1/2

4. sin2 θ + cos2 θ = 1

Calculation:

sin 75° + sin 15°

⇒ sin (90° - 15°) + sin 15°

⇒ cos 15° + sin 15°

⇒ sin 15° + cos 15° = k (let)

​According to the concept,

sin2 15° + cos2 15° = 1

⇒ (sin 15° + cos 15°)2 - 2.sin 15°.cos 15° = 1

⇒ k2 - sin (2 × 15)° = 1

⇒ k2 - sin 30° = 1

⇒ k2 - 1/2 = 1 

⇒ k2 = 1 + 1/2

⇒ k2 = 3/2

⇒ k = 

∴ The value of sin 75° + sin 15° is .

Shortcut Trick

We know, sin C + sin D = 

sin 75° + sin 15 =  = 2 × sin 45° × cos 30° = 2 ×  ×  = 

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