a: x^3-2x-4=0

=>x^3-2x^2+2x^2-4x+2x-4=0

=>(x-2)(x^2+2x+2)=0

=>x-2=0

=>x=2

b: 2x^3-12x^2+17x-2=0

=>2x^3-4x^2-8x^2+16x+x-2=0

=>(x-2)(2x^2-4x+1)=0

=>x=2; \(x=\dfrac{4\pm\sqrt{14}}{2}\)

Chọn D

Bài 2 

P(x) + Q(x) =  x³ – 6x + 2 + 2x² - 4x³ + x - 5 =  - 3x³ + 2x² – 5x - 3 

P(x) - Q(x) = x³ – 6x + 2 - 2x² + 4x³ - x + 5 = 5x³ − 2x² − 7x+7

Bai 3

a)(x-8)(x³+8)=0

=>x-8=0 hoac x³+8=0

=>x   =8 hoac x³    =-8

=>x   =8 hoac x     =-2

Vậy x=8 hoặc x=-2

b)(4x-3)-(x+5)=3(10-x)

=>4x-3-x-5=30-3x

=>4x-x+3x=30+3+5

=>x(4-1+3)=38

=>6x         =38

=>x           =\(\dfrac{38}{6}\)

=>x           =\(\dfrac{19}{3}\)

Vậy x=\(\dfrac{19}{3}\)

a) Đặt A(x)=0

\(\Leftrightarrow-4x-5=0\)

\(\Leftrightarrow-4x=5\)

hay \(x=-\dfrac{5}{4}\)

b) Đặt B(x)=0

\(\Leftrightarrow3\left(2x-1\right)-2\left(x+1\right)=0\)

\(\Leftrightarrow6x-3-2x-2=0\)

\(\Leftrightarrow4x=5\)

hay \(x=\dfrac{5}{4}\)

`M(x)-N(x)=`\((-x^3+3x^2+5x+4)-(x^3+4x^2+6x-5)\)

`=-x^3+3x^2+5x+4-x^3-4x^2-6x+5`

`= (-x^3-x^3)+(3x^2-4x^2)+(5x-6x)+(4+5)`

`= -2x^3-x^2-x+9`

`@`\(\text{dn inactive.}\)

a: Đặt A(x)=0

=>x²(x-1)=0

=>x=0 hoặc x=1

b: Đặt B(x)=0

=>2x+1-1/2x+1=0

=>3/2x=-2

hay x=-2:3/2=-4/3

c: \(3x^2+12\ge12>0\)

nên M(x) vô nghiệm

e: Đặt N(x)=0

=>(x-2)(x-4)=0

=>x=2 hoặc x=4

a: P(x)=6x^3-4x^2+4x-2

Q(x)=-5x^3-10x^2+6x+11

M(x)=x^3-14x^2+10x+9

b: \(C\left(x\right)=7x^4-4x^3-6x+9+3x^4-7x^3-5x^2-9x+12\)

=10x^4-11x^3-5x^2-15x+21