упростите -квадратный корень под ним (sint+cost)^2-1/tgt

((sint+cost)²-1)/tgt=(sin²t+2*sint*cost+cos²t-1)/tgt==((sin²t+cos²t)+2*sint*cost-1)/tgt=(1+2*sint*cost-1)/tgt==2*sint*cost/(sint/cost)=2*cos²t.