F (x) = sin (2x+1) - 3cos (1-x)

может так

f (x) = sin (2x+1) - 3cos (1-x)

f (x) + 3 cos (1-x) = sin (2 x+1)

f (x) = - sin (1) sin^2 (x) - 3sin (1) sin (x) - 3cos (1) cos (x) + sin (1) cos^2 (x) + 2cos (1) sin (x) cos (x)

f (x) = - 3/2 e^ (i-i x) - 3/2 e^ (-i+i x) + 1/2 i e^ (-i-2 i x) - 1/2 i e^ (i+2 i x)