P(x) + Q(x) + H(x) = (2x4 - x - 2x3 + 1) + (5x2 - x3 + 4x) + (-2x4 + x2 + 5)
= 2x4 - x - 2x3 + 1 + 5x2 - x3 + 4x - 2x4 + x2 + 5
= -3x3 + 6x2 + 3x + 6
P(x) - Q(x) - H(x) = (2x4 - x - 2x3 + 1) - (5x2 - x3 + 4x) - (-2x4 + x2 + 5)
= 2x4 - x - 2x3 + 1 - 5x2 + x3 - 4x + 2x4 - x2 - 5
= 4x4 - x3 - 6x2 - 5x - 4