For any real θ the max value of cos2(cosθ)+sin2(sinθ)=
1+sin21
1+cos21
1
2
Let f(θ)=cos2(cosθ)+sin2(sinθ)We have -1≤cosθ≤1 and -1≤sinθ≤1∴ cos21≤cos2(cosθ)≤1 and 0≤sin2(sinθ)≤sin21
Max value of f(θ)=1+sin21