Как решить такой пример : cos x+ cos2x + cos3x+cos4x+ …+ cosnx в паскале? .

1. cosx + cos2x + cos3x = 0
cos2x + (cosx + cos3x) = 0
cos2x + 2 cos (3x + x / 2) cos (3x - x / 2) = 0
cos2x + 2 cos2xcosx = 0
cos2x (1 + 2cosx) = 0
cos2x = 0 или 1 + 2cosx = 0
 
1) cos2x = 0
cos2x = cosπ/2 + πn
2x = π/2 + πn
x = π/4 + πn/2; n принадлежит Z.
 
2) 1 + 2 cosx = 0
cos x = -1/2
x1 = 2π/3 + 2πn;
x2 = -2π/3 + 2πn;
n принадлежит Z.
 
2. на отр-ке (0;2π): 
1) π/4, 3π/4, 5π/4, 7π/4
2) 2π/3, 4π/3