2) Considerando os polinômios
A = 6x3 + 5x2 – 8x + 15, B = 2x3 – 6x2 – 9x + 10 e C = x3 + 7x2 + 9x + 20. Calcule:
a) A + B + C
b) A – B – C
c) B – C