4)sin²(π/4)-2cos²(π/3)-5tg²(π/4)=(√2/2)²-2.(1/2)²-5.(1)²=1/2-1/2-5=-5
5)(5+9-1)/(1-1-1)=13/(-1)=-13
(ctg(π/4)=1, ctg(π/6)=√3, tg(π/4)=1, cos(π/3)=1/2, sin(π/6)=1/2)
6)(a³-b³-0)/(a²+ab+b²)=(a³-b³)/(a²+ab+b²)=(a-b)(a²+ab+b²)/(a²+ab+b²)=a-b
(A³-B³=(A-B)(A²+AB+B²))
(cos(π/2)=0, cos0=1, cos(π/4)=(√2)/2)