For any real θ the maximum value of cos2(cosθ)+sin2(sinθ) is
1
1+sin21
1+cos21
2+cos21
cos2(cosθ)+sin2(sinθ)
+sin2(cosθ)−sin2(cosθ)
=1+sin2(sinθ)−sin2(cosθ), which is maximum when cosθ=0,sinθ=1