Find the exact value of sin 9π/4.

Is my working correct?
9π/4 = 8π/4 + π/4
= 2π + π/4
angle is in the 1st quadrant, and sinθ is positive in the 1st quadrant
∴ sin 9π/4 = sin (2π + π/4)
= sin π/4
= 1/√2

Question

Find the exact value of sin 9π/4.

Is my working correct?
9π/4 = 8π/4 + π/4
         = 2π + π/4
angle is in the 1st quadrant, and sinθ is positive in the 1st quadrant
∴ sin 9π/4 = sin (2π + π/4)
                 = sin π/4
                 = 1/√2

marco26 · Answer

That's right. Though you might want to rationalize the denominator for simplification.

anonymous · Answer

will do, thanks