Question

Find the value of sin 660 degree + sin 780 degrees

Answer 1

Answer:

sin 780° = sin 60° = √3/2

sin 660° = 300° = -√3/2

sin 420° = 60° = √3/2

sin 780 - sin 660 - sin 420 + sin 60

= √3/2 - (-√3/2) - √3/2 +√3/2

= 0

Answer 2

Answer:

0

Step-by-step explanation:

sin 660° = sin (660° - 360° - 360°)

             = sin (-60°)   (IV quadrant where sin and sec will be negative)    

                                  (sin 60° = √3/2)

              =   - √3/2

sin 780° = sin (780°-360°-360°)

              = sin 60° (Lies in the I quadrant where sin is positive)

              = √3/2

Hence sin660° +sin 780° =   (-√3/2)+(√3/2)

                                          = 0