คำตอบ - Trigonometry

The period of trigonometric functions is 360 degrees.

$$\cos \left(630°\right)=\cos \left(630-360°\right)$$

Subtracting one integer from another.

$$\cos \left(630-360°\right)=\cos \left(270°\right)$$

Reflecting the number with respect to 360 degrees.

$$\cos \left(270°\right)=\cos \left(360-90°\right)$$

The period of trigonometric functions is 360 degrees.

$$\cos \left(360-90°\right)=\cos \left(360-90-360°\right)$$

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

$$\cos \left(360-90-360°\right)=\cos \left(-90°\right)$$

Computing the cosine of a negative angle.

$$\cos \left(-90°\right)=\cos \left(90°\right)$$

Computing the cosine of 90 degrees.

$$\cos \left(90°\right)=0$$