Question

Tìm x, biết :
a, ( x +2 ) ( x^2 - 2x + 4 ) - x( x + 3 ) ( x - 3) = 26
b, ( x - 3 ) ( x^2 + 3x + 9 ) - x( x - 4 ) ( x + 4 ) = 21
c, ( 2x -1 ) ( 4x^2 + 2x + 1 ) - 4x(2x^2 - 3 ) = 23

Answer 1

a/\(\left(x+2\right)\left(x^2-2x+4\right)-x\left(x+3\right)\left(x-3\right)=26\)

↔ \(x^3+2^3\)\(-x\left(x^2-3^2\right)\)= 26

↔\(x^3+8-x^3+9x=26\)

↔\(9x=18\leftrightarrow x=2\)

Vậy x=2

b/\(\left(x-3\right)\left(x^2+3x+9\right)-x\left(x-4\right)\left(x+4\right)=21\)

\(\Leftrightarrow x^3-3^3-x\left(x^2-4^2\right)=21\)

\(\Leftrightarrow x^3-9-x^3+16x=21\)

\(\Leftrightarrow16x=30\)

\(\Leftrightarrow x=\frac{15}{8}\)

Vậy \(x=\frac{15}{8}\)

c/\(\left(2x-1\right)\left(4x^2+2x+1\right)-4x\left(2x^2-3\right)=23\)

↔\(\left(2x\right)^3-1^3-4x\left(2x^2-3\right)=23\)

↔\(8x^3-1-8x^3+12x=23\)

↔\(12x=24\leftrightarrow x=2\)

Vậy x=2

Answer 2

a, (x + 2)(x² - 2x + 4 ) - x(x + 3)(x - 3) = 26

<=> x³ + 8 - x(x² - 9) = 26

<=> x³ + 8 - x³ + 9x = 26

<=> 9x - 18 = 0

<=> 9x = 18

<=> x = 2
b, (x - 3)(x² + 3x + 9) - x(x - 4)(x + 4) = 21

<=> x³ - 27 - x(x² - 16) = 21

<=> x³ - 27 - x³ + 16x = 21

<=> 16x - 48 = 0

<=> 16x = 48

<=> x = 3
c, (2x - 1)(4x² + 2x + 1) - 4x(2x² - 3) = 23

<=> 8x³ - 1 - 8x³ + 12x = 23

<=> 12x - 24 = 0

<=> 12x = 24

<=> x = 2

Answer 3

\(\left(x+2\right)\left(x^2-2x+4\right)-x\left(x+3\right)\left(x-3\right)=26\)

\(< =>x^3-2x^2+4x+2x^2-4x+8-x\left(x^2-9\right)-26=0\)

\(< =>x^3+8-x^3+9x-26=0\)

\(< =>9x-18=0< =>x=2\)

Answer 4

\(\left(x-3\right)\left(x^2+3x+9\right)-x\left(x-4\right)\left(x+4\right)=21\)

\(< =>x^3+3x^2+9x-3x^2-9x-27-x\left(x^2-16\right)-21=0\)

\(< =>x^3-27-x^3+16x-21=0\)

\(< =>16x-48=0< =>x=3\)

Answer 5

\(\left(2x-1\right)\left(4x^2+2x+1\right)-4x\left(2x^2-3\right)=23\)

\(< =>8x^3+4x^2+2x-4x^2-2x-1-8x^3+12x-23=0\)

\(< =>12x-24=0< =>x=2\)