Cos²x=0.5
найдём sin²x
выразим cos²x=1-sin²x
1-sin²x=0.5
sin²x=0.5
6tg²x-2=6sin²x/cos²x -2=6*0.5/0.5-2=6-2=4
Sin(6π-π/2)=sin(-π/2)=-1
cos(-13π/4)=cos(13π/4)=cos(3π+π/4)=cos(π+π/4)=-cosπ/4=-√2/2
sin(2π+π/3)=sinπ/3=√3/2
<span>cos(-13π/6)=cos(13π/6)=cos(2π+π/6)=cos(π/6)=</span>√3/2
(x-2)^2-(x-1)(x+2)=x²-4x+4-(x²-x+2x-2)=x²-4x+4-x²+x-2x+2=-5x+6