คำตอบ - Trigonometry

The period of trigonometric functions is 360 degrees.

$$\cos \left(1260°\right)=\cos \left(1260-360°\right)$$

Subtracting one integer from another.

$$\cos \left(1260-360°\right)=\cos \left(900°\right)$$

The period of trigonometric functions is 360 degrees.

$$\cos \left(900°\right)=\cos \left(900-360°\right)$$

Subtracting one integer from another.

$$\cos \left(900-360°\right)=\cos \left(540°\right)$$

The period of trigonometric functions is 360 degrees.

$$\cos \left(540°\right)=\cos \left(540-360°\right)$$

Subtracting one integer from another.

$$\cos \left(540-360°\right)=\cos \left(180°\right)$$