Question

Find the exact value, without a

calculator.
570
570
sin
6
sin
12
2
'?]+/

Answer 1

√(2 + √3)/4

Explanation:

Sine 5π/12 = Sine (5π/6)/2

Recall

π = 180°

Thus,

Sine (5π/6)/2 = Sine (5×180 /6)/2

= Sine 150/2

Recall

Sine θ/2 = √(1 – Cos θ)/2

Thus,

Sine 150/2 = √(1 – Cos 150)/2

But, Cosine is negative in the 2nd quadrant. Thus,

Cos 150 = – Cos 30 = –√3/2

Thus,

√(1 – Cos 150)/2 = √(1 – –√3/2 )/2

= √(1 + √3/2 )/2

= √[(2 + √3)/2 ÷ 2]

= √[(2 + √3)/2 × 1/2]

= √(2 + √3)/4

Therefore,

Sine 5π/12 = √(2 + √3)/4