Sec theta sin thetatan theta cot theta sin2 theta csc2 the
     Sec theta sin theta/tan theta + cot theta = sin^2 theta  csc^2 theta tan^2 theta - 1 = tan^2 theta  sec x - tan x sin x = 1/sec x 
  
  Solution
13) sectheta*sintheta/(tantheta + cotheta) = sin^2theta
LHS : (sintheta/costheta)/( tantheta + 1/tantheta)
tantheta*tantheta/(1+tan^2theta)
tan^2theta/sec^2theta
sin^2theta/cos^2theta*sec^2theta
sin^2theta
RHS

