Все на картинке
d^2=a^2+b^2+c^2 a=sqrt(6)*x; с=sqrt(5)*x b=sqrt(10)*x (2sqrt(21))^2=6x^2+5x^2+10x^2 x^2=4 x=2 a) a=2sqrt(6) c=2sqrt(5) b=2sqrt(10) б) sin phi=c/d=2sqrt(5)/2sqrt(21)=sqrt(5/21)