Let \( P=\{\theta\in[0,4\pi]:\tan^2\theta=1\} \) and \( S=\{a\in\mathbb{Z}: 2(\cos^8\theta-\sin^8\theta)\sec 2\theta=a^2,\; \theta\in P\} \). Then \( n(S) \) is:
\( 0 \)
\( 1 \)
\( 2 \)
\( 3 \)