how do i do this

how do i do this

cos-1(8/17)

A)  $cos^{ -1}(a) \ means \ arccos \ (a)$    Normal pocket calculator

$cos^{-1}(\frac{8}{17})=arccos(\frac{8}{17})=arccos (0.470588235)=61.93°$

B)  $cos^{ -1}(a) \ means \ \frac{1}{cos (a)}$

$\large cos^{-1}(\frac{8}{17}deg)=\frac{1}{cos(\frac{8}{17}deg)}=\frac{1}{1}=1$

  !