1. The problem asks why the cosine function is positive in the first and fourth quadrants of the unit circle. 2. Recall that cosine of an angle $\theta$ in the unit circle is the $x$-coordinate of the point on the circle at angle $\theta$ from the positive $x$-axis. 3. In the **first quadrant** ($0^\circ < \theta < 90^\circ$ or $0 < \theta < \frac{\pi}{2}$), both $x$ and $y$ coordinates of the point are positive as it lies in the top-right quadrant. 4. Since cosine corresponds to the $x$-coordinate and $x > 0$ there, cosine is positive in the first quadrant. 5. In the **fourth quadrant** ($270^\circ < \theta < 360^\circ$ or $\frac{3\pi}{2} < \theta < 2\pi$), the point lies in the bottom-right quadrant where $x$ is still positive but $y$ is negative. 6. Therefore, the cosine function, representing the $x$-coordinate, remains positive in the fourth quadrant. 7. In summary, cosine is positive where the unit circle points have positive $x$ values, which happens in the first and fourth quadrants.