i) Tomemos $arcsen \frac{3}{5}$ como $\alpha$ e $arccos \frac{4}{5}$ como $\theta$ $\alpha = arcsen \frac{3}{5} \therefore sen(\alpha) = \frac{3}{5} \Rightarrow cos(\alpha) = \frac{4}{5}$ $\theta = arccos \frac{4}{5} \therefore cos(\theta) = \frac{4}{5} \Rightarrow sen(\theta) = \frac{3}{5}$ ii) $cos(arcsen(\frac{3}{5})+arccos(\frac{4}{5})) = cos(\alpha + \theta)$ $cos(\alpha + \theta) = cos(\alpha).cos(\theta) - sen(\alpha).sen(\theta) = \frac{4}{5}.\frac{4}{5} - \frac{3}{5}.\frac{3}{5}$ $\therefore cos(arcsen(\frac{3}{5})+arccos(\frac{4}{5})) = \frac{7}{25}$