По теореме косинусов:
c^2=a^2+b^2-2abcos γ
с^2=12^2+8^2-2*12*8*cos60 °
c^2=144+64-2*12*8*(1/2)
c^2=112
c=sqrt(112)
c=2sqrt(38)
sin γ =sin60 ° =sqrt(3)/2
По теореме синусов
a/sin α =c/sin γ ⇒ sin α =a*sin γ /c=12*sqrt(3)/4sqrt(38)=[b]3sqrt(3)/sqrt(38)[/b]
c/sin γ =b/sin β ⇒ sin β= b*sin γ /c=8*sqrt(3)/4sqrt(38)=2sqrt(3)/sqrt(38)
2,
α + β + γ =180 ° ⇒ α =180 ° - β - γ =180 ° -30 ° -45 ° =105 °
sin α =sin105 ° =sin(60 ° +45 ° )=sin60 ° *cos 45 ° +cos60 ° * sin45 ° =sqrt(2)*(sqrt(3)+1)/4
По теореме синусов
a/sin α =b/sin β ⇒ b=a*sin β /sin α =5sin30 ° /sqrt(2)*(sqrt(3)+1)/4=[b]5sqrt(2)/(sqrt(3)+1)[/b]
a/sin α =c/sin γ ⇒ c=a*sin γ /sin α=5*sin45 ° /sqrt(2)*(sqrt(3)+1)/4=[b]10/(sqrt(3)+1)[/b]