Друзья, прошу помочь с 2-мя номерами по тригонометрии =)

1
[sin(2π+π/4)-cos(3π-π/4)]*[-sin(4π-π/2)]:cos(9π+π/3)=
=(sinπ/4+cosπ/4)*sinπ/2:(-cosπ/3)=(√2/2+√2/2)*1:(-1/2)=
=√2*(-2)=-2√2
2
$\sqrt{(1-cosa)/(1+cosa)} =tg(a/2)$
$\sqrt{(1+cosa)/(1-cosa)} =ctg(a/2)$
tg(a/2)+ctg(a/2)=sin(a/2)/cos(a/2)+cos(a/2)/sin(a/2)=
=(sin²(a/2)+cos²(a/2))/(cos(a/2)sin(a/2)=2/sina
sina=-4/5 2:(-4/5)=-2,5