If $\theta=\frac{2 \pi}{3}$, then
\[
\begin{array}{l}
\sin (\theta)= \\
\cos (\theta)=
\end{array}
\]

Step 1 ：Given that the angle \(\theta=\frac{2 \pi}{3}\), we need to find the sine and cosine of this angle.

Step 2 ：The sine and cosine of an angle can be found using the unit circle. The unit circle is a circle with a radius of 1 that is centered at the origin of the coordinate plane. The x-coordinate of a point on the unit circle represents the cosine of the angle formed by the positive x-axis and the line segment connecting the origin and the point. The y-coordinate represents the sine of the angle.

Step 3 ：For \(\theta=\frac{2 \pi}{3}\), we can find the sine and cosine values by locating the point on the unit circle that corresponds to this angle.

Step 4 ：The sine and cosine values for \(\theta=\frac{2 \pi}{3}\) are approximately 0.866 and -0.5 respectively. These values are consistent with the location of the point on the unit circle that corresponds to this angle.

Step 5 ：Final Answer: The sine and cosine of \(\theta=\frac{2 \pi}{3}\) are approximately \(\boxed{0.866}\) and \(\boxed{-0.5}\) respectively.