\(x\left(x^2+x+1\right)=8\left(x^2+x+1\right)\)

\(\Leftrightarrow\left(x-8\right)\left(x^2+x+1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-8=0\\x^2+x+1=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=8\\\left(x+\dfrac{1}{2}\right)^2+\dfrac{3}{4}=0\left(vô-nghiệm\right)\end{matrix}\right.\)

1/8x + 3/8x - 5/3 = 2

=> (1/8 + 3/8)x = 2+5/3

=> 1/2x = 11/3

=> x = 11/3:1/2

=> x = 22/3

Vậy x = 22/3

\(x^4-8x^3+11x^2+8x-12=0\)

\(\Leftrightarrow\left(x^2-1\right)\left(x^2-8x+12\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x-6\right)\left(x-2\right)=0\)

\(\Leftrightarrow x=\left\{1;-1;6;2\right\}\)

\(x^4-8x^3+11x^2+8x-12=0\)

\(\Leftrightarrow x^4-x^3-7x^3+7x^2+4x^2-4x+12x-12=0\)

\(\Leftrightarrow\left(x^4-x^3\right)-\left(7x^3-7x^2\right)+\left(4x^2-4x\right)+\left(12x-12\right)=0\)

\(\Leftrightarrow x^3\left(x-1\right)-7x^2\left(x-1\right)+4x\left(x-1\right)+12\left(x-1\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x^3-7x^2+4x+12\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x^3+x^2-8x^2-8x+12x+12\right)=0\)

\(\Leftrightarrow\left(x-1\right)[x^2\left(x+1\right)-8x\left(x+1\right)+12\left(x+1\right)]=0\)

\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x^2-8x+12\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(x-2\right)\left(x-6\right)=0\)

\(\Leftrightarrow\)x - 1 =0 ; x + 1 = 0 ; x - 2 =0 hoặc x - 6 = 0

\(\Leftrightarrow\)x = 1 ; x = -1 ; x = 2 ; x=6

lỗi đề

Ta có 3 x 2 + 8x + 5 = 0

ó 3 x 2 + 3x + 5x + 5 = 0 ó 3x(x + 1) + 5(x + 1) = 0

ó (3x + 5)(x + 1) = 0 

Vậy  x = - 5 3 ;   x = - 1

Đáp án cần chọn là: A

\(8x\left(x-3\right)-8\left(x-1\right)\left(x+1\right)=20\)

\(\Leftrightarrow8x^2-24x-8\left(x^2-1\right)=20\)

\(\Leftrightarrow8x^2-24x-8x^2+8=20\)

\(\Leftrightarrow\left(8x^2-8x^2\right)+\left(-24x+8\right)=20\)

\(\Leftrightarrow-24x=20-8\)

\(\Leftrightarrow-24x=12\)

\(\Leftrightarrow x=12:\left(-24\right)\)

\(\Leftrightarrow x=-\frac{1}{2}\)

Vậy: \(x=-\frac{1}{2}\)

\(8x\left(x-2\right)-8\left(x-1\right)\left(x+1\right)=20\)

\(\Leftrightarrow8x^2-24x-8\left(x^2-1\right)=20\)

\(\Leftrightarrow8x^2-24x-\left(8x^2-8\right)=20\)

\(\Leftrightarrow8x^2-24x-8x^2+8=20\)

\(\Leftrightarrow-24x+8=20\)

\(\Leftrightarrow-24x=20-8\)

\(\Leftrightarrow-24x=12\)

\(\Leftrightarrow x=-\frac{1}{2}\)

Ta có:

8x(x - 3) - 8(x - 1)(x + 1) = 20

=> 8x² - 24x - 8(x² - 1) = 20

=> 8x² - 24x - 8x² + 8 = 20

=> -24x = 12

=> x = 12/-24 = -2

     \(2x^3+x^2-8x-4=0\)

\(\Leftrightarrow\)\(x^2\left(2x+1\right)-4\left(2x+1\right)=0\)

\(\Leftrightarrow\)\(\left(2x+1\right)\left(x^2-4\right)=0\)

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

đến đây bạn làm tiếp nha

\(2x^3+x^2-8x-4=0\)

\(x^2\left(2x+1\right)-4\left(2x+1\right)=0\)

\(\left(x^2-4\right)\left(2x+1\right)=0\)

\(1.x^2-4=0\)

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

\(\Rightarrow x=\pm2\)

\(2.2x+1=0\)

\(x=-\frac{1}{2}\)

\(2x^3+x^2-8x-4=0\)

\(\Leftrightarrow x^2.\left(2x+1\right)-4\left(2x+1\right)=0\)

\(\Leftrightarrow\left(2x+1\right)\left(x^2-4\right)=0\)

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

\(\Leftrightarrow\)2x + 1 = 0 => x = -1/2

Hoặc x - 2 = 0 => x = 2

Hoặc x + 2 = 0 => x = -2

Vậy x = -1/2 hoặc x = 2 hoặc x = -2

7/5 x X + 3/8 x X= 9

X x (7/5 +3/8)=9

X x 71/40 = 9

X             = 9:71/40

X             = 360/71

     \(\frac{7}{15}X+\frac{3}{8}X=9\)

     \(\left(\frac{7}{15}+\frac{3}{8}\right)X=9\) 

\(\left(\frac{56}{120}+\frac{45}{120}\right)X=9\)

                  \(\frac{101}{120}X=9\)

                          \(X=9:\frac{101}{120}\)

                          \(X=9x\frac{120}{101}\)

                          \(X=\frac{1080}{101}\)