Question 998935
Find, or derive, the double angle cosine formulas, and pick the one which uses only {{{cos(t)}}}.  This is the one:  {{{cos(2t)=2*cos^2(t)-1}}}.


LeftHandSide


{{{2/(1+2*cos^2(t)-1)}}}


{{{2/(2*cos^2(t))}}}


{{{1/cos^2(t)}}}


and according to definition
{{{sec^2(t)}}}