Final answer:
The expression cos^2 x sin^2 x cannot be simplified to cos x using standard trigonometric identities. The provided options do not lead to a simplification of the original expression.
Step-by-step explanation:
The expression cos^2 x sin^2 x cannot be simplified to just cos x. To simplify cos^2 x sin^2 x, you need to apply trigonometric identities. However, none of the provided options (a) cos^2 x, b) sin^2 x, c) cos x sin x, d) cos x + sin x) result in cos^2 x sin^2 x by the application of standard trigonometric identities. The simplest form of cos^2 x sin^2 x remains as is or could be written in terms of sine or cosine using the identity sin^2(x) = 1 - cos^2(x) or cos^2(x) = 1 - sin^2(x), but neither of these forms will simplify further to any of the provided options.