Найти sin3a-cos3a, если sina-cosa=m

81 (sin^3 (a) + cos^3 (a)) = 81 (sin (a) + cos (a)) (sin^2 (a) - sin (a) cos (a) + cos^2 (a)) = (81/3) (1 - 0.5sin (2a)) = (*)

sin^2 (a) + cos^2 (a) + sin (2a) = 1 + sin (2a) = 1/9 = > sin (2a) = 1/9 - 1 = - 8/9

(*) = (81/3) (1 + 8/18) = (81/3) (26/18) = 39