The derivative of \( \cos^{-1}x \) is \( -\frac{1}{\sqrt{1 - x^2}} \), which is important for solving problems involving inverse trigonometric functions.
Step 1: Using the derivative of the inverse cosine function.
The derivative of \( \cos^{-1}x \) is a standard result:
\[
\frac{d}{dx} \left( \cos^{-1}x \right) = -\frac{1}{\sqrt{1 - x^2}}
\]
Step 2: Conclusion.
Thus, the derivative of \( \cos^{-1}x \) is \( -\frac{1}{\sqrt{1 - x^2}} \).