Considerando as funções $$\mathrm{arcsen}:[-1,+1]\to [-\pi /2,\pi /2]\text{ e }\arccos :[-1,+1]\to [0,\pi ],$$ assinale o valor de $\cos \left(\mathrm{arcsen}\frac{3}{5}+\arccos \frac{4}{5}\right)$