a.
- Tính P(1):
P(1) = 5(1)^4 + 4(1)^3 - 5(1)^2 + 2(1) - 9
P(1) = 5 + 4 - 5 + 2 - 9
P(1) = 2

- Tính P(2):
P(2) = 5(2)^4 + 4(2)^3 - 5(2)^2 + 2(2) - 9
P(2) = 5(16) + 4(8) - 5(4) + 4 - 9
P(2) = 80 + 32 - 20 + 4 - 9
P(2) = 87

- Tính P(-2):
P(-2) = 5(-2)^4 + 4(-2)^3 - 5(-2)^2 + 2(-2) - 9
P(-2) = 5(16) + 4(-8) - 5(4) - 4 - 9
P(-2) = 80 - 32 - 20 - 4 - 9
P(-2) = 15

b.
- Tính P(x) + Q(x):
P(x) + Q(x) = (5x^4 + 4x^3 - 5x^2 + 2x - 9) + (-4x^4 + 2x^3 - 4x - 12)
P(x) + Q(x) = 5x^4 + 4x^3 - 5x^2 + 2x - 9 - 4x^4 + 2x^3 - 4x - 12
P(x) + Q(x) = x^4 + 6x^3 - 5x^2 - 2x - 21

- Tính P(x) - Q(x):
P(x) - Q(x) = (5x^4 + 4x^3 - 5x^2 + 2x - 9) - (-4x^4 + 2x^3 - 4x - 12)
P(x) - Q(x) = 5x^4 + 4x^3 - 5x^2 + 2x - 9 + 4x^4 - 2x^3 + 4x + 12
P(x) - Q(x) = 9x^4 + 2x^3 - 5x^2 + 6x + 3

- Tính Q(x) - P(x):
Q(x) - P(x) = (-4x^4 + 2x^3 - 4x - 12) - (5x^4 + 4x^3 - 5x^2 + 2x - 9)
Q(x) - P(x) = -4x^4 + 2x^3 - 4x - 12 - 5x^4 - 4x^3 + 5x^2 - 2x + 9
Q(x) - P(x) = -9x^4 - 2x^3 + 5x^2 - 6x - 3