cos200 ° =p ⇒ -cos20 ° =p ⇒ [b]cos20 ° =-p[/b]
p <0
ctg70 ° =ctg(90 ° -20 ° )=tg20 °
1+tg^220 ° =1/cos^220 ° ⇒
tg^220 ° = (1/cos^220°)-1 ⇒ (1/(-p)^2 ) - 1=(1-p^2)/p^2
tg20 ° =sqrt(1-p^2)/|p|
p<0
|p|=-p
[b]tg20 ° =-sqrt(1-p^2)/p[/b]
3x^2+8x-1=0
По теореме Виета:
a+b=-8/3
a*b=-1/3
(a/b^2)+(b/a^2)=(a^3+b^3)/(ab)^2=(a+b)*(a^2-ab+b^2)/(ab)^2
a^2+b^2=(a+b)^2-2ab
(a/b^2)+(b/a^2)=(-8/3)*((-8/3)^2-3*(-1/3))/(-1/3)^2=
=-(8/3)*((64/9)+1)/(1/9)=
=-(8/3)*73=-584/3