We have sinθ + cosθ = √2 sin(θ + π/4) ≤ √2 since the maximum value of sin(θ + π/4) = 1
But √2 < π/2; (√2 is approximately 1.414 and π/2 is approximately 1.59). Therefore,
cosine being a decreasing function in first quadrant. That is
cos(sinθ) > sin(cosθ)