Cho hai đa thức P(x) = 5x4 + 3x – 2x3 – 6 + 7x2; Q(x) = –3x + 12x2 + 9 – 4x4a) Tính P(x) + Q(x)    b) Tính P(x) �

* Hướng dẫn giải

a) P(x) + Q(x) = (5x⁴ + 3x – 2x³ – 6 + 7x²) + (–3x + 12x² + 9 – 4x⁴)

                        = 5x⁴ + 3x – 2x³ – 6 + 7x² – 3x + 12x² + 9 – 4x⁴

                        = 5x⁴ – 4x⁴ – 2x³  + 7x² + 12x² + 3x – 3x – 6 + 9

                        = x⁴ – 2x³  + 19x² + 3

b) P(x) + Q(x) = (5x⁴ + 3x – 2x³ – 6 + 7x²) + (–3x + 12x² + 9 – 4x⁴)

                        = 5x⁴ + 3x – 2x³ – 6 + 7x² – 3x + 12x² + 9 – 4x⁴

                        = 5x⁴ – 4x⁴ – 2x³  + 7x² + 12x² + 3x – 3x – 6 + 9

                        = x⁴ – 2x³  + 19x² + 3