Rút gọn: A = (cos7x - cos8x - cos9x + cos10x) / (sin7x - sin8x - sin9x + sin10x); B = (sin2x + 2 sin3x + sin4x) / (sin3x + 2 sin4x + sin5x); C = (1 + cosx + cos2x + cos3x) / (cosx + 2 cos^2 x - 1)

Rút gọn:
a, A = (cos7x - cos8x - cos9x + cos10x) / (sin7x - sin8x - sin9x + sin10x)
b, B = (sin2x + 2 sin3x + sin4x) / (sin3x + 2 sin4x + sin5x)
c, C = (1 + cosx + cos2x + cos3x) / (cosx + 2 cos^2 x - 1)
d, D = (sin4x + sin5x + sin6x) / (cos4x + cos5x + cos6x)