The cosine function is even, meaning that $\cos(-\theta) = \cos(\theta)$.

Thus: $\cos\left(-\frac{x}{2}\right) = \cos\left(\frac{x}{2}\right).$

If you have any further context or constraints to consider, feel free to share!

Would you like further details or have additional questions?

Here are 5 related questions to deepen your understanding:

1. How does the even property of cosine compare with sine's odd property?
2. What is the domain and range of the cosine function?
3. How does cosine relate to the unit circle?
4. How do we compute $\cos(-x/2)$ if $x$ is given in radians or degrees?
5. What happens to $\cos(-x/2)$ if we scale $x$ differently, such as multiplying it by a constant?

Tip: Remember that cosine is symmetric about the $y$-axis, making it easy to compute values for negative angles.