a) Cho hai đa thức:A(x) = 5x3 + 3x2 – 2x – 6 và B(x) = 2x3 – 3x2 + 6x – 1 Tính: A(x) + B(x); A(x) – B(x) b) Tính: (x^2-2x+3).(x-4)

a)Ta có A(x)+B(x)=( 5x³+3x²-2x-6)+(2x³-3x²+6x-1)

= 5x³+3x²-2x-6+2x³-3x²+6x-1

=(5x³+2x³)+(3x²-3x²)+(-2x+6x)+(-6-1)

=7x³+4x-7

Ta có A(x)-B(x)=( 5x³+3x²-2x-6)-(2x³-3x²+6x-1)

=5x³+3x²-2x-6-2x³+3x²-6x+1

=(5x³-2x³)+(3x²+3x²)+(-2x-6x)+(-6+1)

=3x³+6x²-8x-5

b)(x²-2x+3)(x-4)

=x(x²-2x+3)-4(x²-2x+3)

=x³-2x²+3x-4x²+8x-12

=x³+(-2x²-4x²)+(3x+8x)-12

=x³-6x²+11x-12