คำตอบ - Trigonometry

The period of trigonometric functions is 360 degrees.

$$\sin \left(660°\right)=\sin \left(660-360°\right)$$

Subtracting one integer from another.

$$\sin \left(660-360°\right)=\sin \left(300°\right)$$

Reflecting the number with respect to 360 degrees.

$$\sin \left(300°\right)=\sin \left(360-60°\right)$$

The period of trigonometric functions is 360 degrees.

$$\sin \left(360-60°\right)=\sin \left(360-60-360°\right)$$

Removing or simplifying the same numbers on the top and bottom of a fraction.

$$\sin \left(360-60-360°\right)=\sin \left(-60°\right)$$

Computing the sine of a negative angle.

$$\sin \left(-60°\right)=-\sin \left(60°\right)$$

Computing the sine of 60 degrees.

$$-\sin \left(60°\right)=-\frac{\sqrt{3}}{2}$$