a) (x+2)(2x²-x-1)
= 2x³-x²-x+4x²-2x-2
= 2x³+3x²-3x-2
b) 4(x²+3)(2x-4)
= 4(2x³-4x²+6x-12)
= 8x³-16x²+24x-48
c) x²(x-1)(x²-x+7)
= x²(x³-x²+7x-x²+x-7)
= x²(x³-2x²+8x-7)
=$x^{5}$-2$x^{4}$+8$x^{3}$-7$x^{2}$
Tìm x
a) (x+1)(x-2)-(x+3)(x-3)=0
⇔ x²-2x+x-2-x²+3x-3x-9=0
⇔ (x²-x²)-(2x-x)-(2+9) = 0
⇔ -x-11=0
⇔ -x = 11
⇔ x = -11
b) 3(x²-x+2)+(x-1)(2-3x)=0
⇔3x²-3x+6+2x-3x²-2+3x=0
⇔(3x²-3x²)-(3x-2x-3x)+(6-2)=0
⇔2x+4=0
⇔2x =-4
⇔ x = -2