b(b^3-b^2+b)-(b^3-b^2+b) =
= b^4-b^3+b^2 -b^3 +b^2-b = b^4 -2b^3 +2b^2 -b
(a/b+b/a+2)*1/(a+b)=a²+b²+2ab/(a+b)ab=(a+b)²/(a+b)ab=a+b/ab=-1-0.2/-1*(-0.2)=-6
X+(x+40)=180
2x+40=180
2x=140
x=70
Cosa=1-2sin²a/2
sin²a/2=(1-cosa)/2=(1+0,8)/2=0,9
sina/2=+-√0,9