cos x = -√1-sin² x = -√1-4/25 = -√21/25 = - √(21)/5
sin 2x+3,8=2sin x cos x+3,8=2(sin x cos x + 1,9) = 2 * ((-2/5)*(-√(21)/5) + 1,9) = 4√(21)+95/25
