1. The problem is to understand why $\cos \frac{\pi}{2} = 0$. 2. Recall that the cosine function relates to the unit circle, where $\cos \theta$ is the x-coordinate of the point on the unit circle at angle $\theta$ radians from the positive x-axis. 3. The angle $\frac{\pi}{2}$ radians corresponds to 90 degrees, which points straight up on the unit circle. 4. At this point, the coordinates are $(0,1)$, so the x-coordinate (cosine) is 0. 5. Therefore, $\cos \frac{\pi}{2} = 0$ because the point lies on the y-axis, where the x-value is zero. 6. This is a fundamental property of the cosine function on the unit circle.