Simplify the expression by using a double-angle formula.
\[
\cos ^{2} 2 \theta-\sin ^{2} 2 \theta
\]
Final Answer: The simplified expression is \(\boxed{\cos(4\theta)}\).
Step 1 :Given the expression \(\cos ^{2} 2 \theta-\sin ^{2} 2 \theta\).
Step 2 :Recognize that this is a difference of squares, which can be factored as \((a-b)(a+b)\).
Step 3 :However, in this case, we can use the double angle formula for cosine, which is \(\cos(2\theta) = \cos^2(\theta) - \sin^2(\theta)\).
Step 4 :Therefore, the given expression can be simplified to \(\cos(4\theta)\).
Step 5 :Final Answer: The simplified expression is \(\boxed{\cos(4\theta)}\).