Question

Find an exact value.

sine of negative eleven pi divided by twelve.


A. square root of six plus square root of two divided by four.

B. negative square root of six minus square root of two divided by four.

C. square root of two minus square root of six divided by four.

D. square root of six minus square root of two divided by four.

Answer 1

(√2 - √6) / 4

C. square root of two minus square root of six divided by four.

Explanation:

sine of negative eleven pi divided by twelve.

We have :

sin(-11π/12)

sin((4 - 15)π / 12) = sin(4π/12 - 15π/12)

sin(4π/12 - 15π/12) = sin(π/3 - 5π/4)

Recall:

Angle difference formula:

sin(A - B) = sinAcosB - sinBcosA

Hence,

sin(π/3 - 5π/4) = sin(π/3) cos(5π/4) − sin(5π/4) cos(π/3)

From trigonometry:

sinπ/3 = √3/2

cos5π/4 = -√2/2

sin5π/4 = -√2/2

cos π/3 = 1/2

(√3/2) (-√2/2) − (-√2/2) (1/2)

-√6/4 - -√2/4

-√6/4 + √2/4

√2/4 - √6/4

(√2 - √6) / 4