คำตอบ - Trigonometry

Reflecting the number with respect to 360 degrees.

$$\sin \left(135°\right)=\sin \left(180-45°\right)$$

Reflecting the sine function with respect to 180 degrees.

$$\sin \left(180-45°\right)=\sin \left(45°\right)$$

Computing the sine of 45 degrees.

$$\sin \left(45°\right)=\frac{\sqrt{2}}{2}$$