Question 983428


You are absolutely right with yours transformations.


The only thing you need to add to it is the equality 


{{{1/cos(x)}}} = {{{sec(x)}}},


which is simply the definition of  {{{sec(x)}}},  and then 


{{{1/cos^2(x)}}} = {{{sec^2(x)}}},


which is the consequence of the definition.


Good luck !