(√21+ √3)^2 - 6√7 21+2√21*√3+3-6√7 24+2*√9*√7-6√7 24+6√7 -6√7
__________________=------------------------------ = --------------------------- =--------------------- = 2
12 12 12 12
((sina-cosa)^2-1+sin4a)/(cos2a+cos4a)=(sina^2-2sinacosa+cosa^2-sina^2-cosa^2+sin4a)/(cos2a+cos4a)=(-2sinacosa+sin4a)/ (cos2a+cos4a)=(-sin2a+2sin2a)/(cos2a+2cos2a)=
(sin2a(-1+2))/(cos2a(1+2)= sin2a/3cos2a=tg2a/3